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Flasking of Orchid Seed and Stem Propagation with Home-Made Equipment
Darrell K. Dixon
16/Aug/96
Email Address: ddixon@es.com
Home Address: 7144 South 2220 East
Salt Lake City, Utah 84121
. INTRODUCTION:
I have been flasking orchid seed, (mostly Phalaenopsis) for about 15
years, using mostly home-made equipment. The following document describes
my process. It is oriented toward sowing seed from one Phalaenopsis seed
pod into 5 flasks, but it can be adapted to other types of orchids or more
seed pods.
. CREDITS:
The information that I am supplying below is by no means completely
original. I have gathered information for books, articles and directly
from other individuals. Through trial and error, I have merged this
information into a procedure that works well for me.
. DOCUMENT REPRODUCTION CONSENT:
This document was written with the intent of distributing free information
to the orchid growing community. I hereby authorize the reproduction in
any form and the free, (except for a reasonable copy fee if necessary)
distribution of this material. This document may not be reproduced or
distributed with the intent of monetary gain. Any modifications or
additions to this material, (except for grammatical corrections) must be
noted as such in the document.
. A REQUEST FOR INPUT FROM OTHERS:
I am always open to comments and suggestions and would like to hear
from others concerning what process works best for them. I would
especially be interested in input concerning the sanitization of
contaminated seed and the sanitization of stem cuttings.
. DISCLAIMER AND CAUTIONS:
The following procedure involves the sanitization of the hands and arms
with a 10% Clorox solution. If you have any sensitivity to Clorox, this
procedure should not be tried.
This procedure uses a pressure cooker to sterilize the flasks and growth
media. A damaged pressure cooker can be deadly. Make sure that it is in
good condition before using it.
. ARE YOU SURE YOU WANT TO SPEND THE TIME REQUIRED TO GROW ORCHIDS FROM SEED:
I strongly recommend that, before you get involved in the flasking process,
you consider the length of time that you will be taking care of the flasks
and seedlings. It takes from 3 to 5 years to get blooming size orchids
from seed. If you believe that you have the tenacity to take care of them
for this long, then I recommend that you give flasking a try.
. LITERATURE:
I consider it essential that a person read up a little on the flasking
process ahead of time. Information can be found in various sources:
. Home Orchid Growing by Rebecca Northen
I have seen this book at the public library, or it can be purchased
through most book stores or the AOS. If a person is into orchids enough
to be doing flasking, they really should own a copy of this book.
. Aaron Hick's Orchid FAQ (Frequently Asked Questions) documents, which are
currently on the computer internet at: ftp://ftp.nmt.edu/pub/orchids/
. WHAT TO CROSS:
It is critical that you know the parentage of the plants that you are
crossing. Don't do crosses with "no-names". If you do, and end up with
something that is really spectacular, it will be worthless if you don't
know its parentage.
I recommend that you only cross species or good quality/awarded hybrids.
I can tell you from sad experience, that 3 to 5 years is a long time to
wait for disappointing results. If you do not have plants of high quality,
check with local orchid growers. You may find some that will be willing
to make a cross for you and let you flask the seed. Of course, they should
be entitled to some of the seedlings. Also, you can find people on the
computer internet who are willing to supply you with pollen from species
or high quality plants.
. DOING THE CROSS:
I am assuming that you know how to do the cross. This information is
covered in Rebecca Northen's book.
. EQUIPMENT AND MATERIAL:
The following equipment and material are needed for the flasking process:
. BEAKER, PYREX, 500 ml:
Used in the preparation of the growth media.
. CLOROX:
For making a 10% Clorox sterilizing solution.
. COTTON BALLS:
For filling the hole in the stoppers.
. DOUBLE BOILER:
Used in the preparation of the growth media.
. FLASKS, ONE QUART, RECTANGULAR:
I use rectangular flasks so that they can lay on their side. I believe
that working with the opening on the side rather then up helps prevent
contamination during the flasking process.
You will need 5 flasks for sowing the seed from one pod and two extra
flasks for holding water.
I obtain my flasks from:
OFE International, Inc.
P.O. Box 164402
Miama, Florida 33116
Phone: (305) 253-7080
FAX: (305) 251-8245
Price in 1996 catalog:
. Flasks, case of 24: $21.85
. Stoppers, Rubber with one hole, case of 24: $9.45
. FOIL, ALUMINUM:
For covering the stoppers and neck of the flask. You will need two
pieces about 6 inches square for each of the 5 flasks that are used
for seed sowing, and one piece for each of the other two flasks.
. GROWTH CHAMBER:
Controlled environment for seed and seedling growth. Described below.
. GROWTH MEDIA:
Media in the flasks that the seed is sown onto. I have tried several
types and have settled on GERMINAL P from Moral Chemical (for
Phalaenopsis). Other GERMINALS are available from Moral for other
types of orchids. All you have to do is add distilled water and heat.
The pH has already been adjusted. They can be contacted at:
Moral Chemical
P.O. Box 1167
Englewood, Florida 34295
Phone: (941) 474-5759
Price from a few years ago:
. Trial size jar (enough for 1000 ml of water or ten 1 quart
flasks): $10.00
. One pound jar (a much larger quantity): $40.00
They operate out of a private home, so don't let this surprise you
if you call them. I recommend that you call them and have them send
you their current information sheet.
. PRESSURE COOKER, 21 QUART:
For sterilizing the flasks and growth media.
. RAZOR BLADES, SINGLE EDGE:
Used to cut open the seed pod. If flasking more than one seed pod,
you must use a different blade for each pod. Otherwise, seed from
one pod may contaminate a different pod.
. SPRAY BOTTLE:
For spraying the 10% Clorox solution in the transfer chamber.
. SKEWERS, BAMBOO:
For distributing the seed over the growth media. They are available
in most grocery stores. If flasking more than one seed pod, you must
use a different skewer for each pod.
. STOPPERS WITH ONE HOLE:
One for each of the flasks that will hold seed.
. TOOTHBRUSH:
For cleaning the seed pod.
. TOWEL, PAPER:
One piece needed for wrapping up the seed pod after it has been cleaned.
. TOWEL, HEAVY CLOTH, LARGE ENOUGH TO COVER BOTTOM OF TRANSFER CHAMBER:
For a clean, water absorbent working surface in the transfer chamber.
. TOWELS, THIN CLOTH, ABOUT 18 INCHES SQUARE:
For wiping things off and covering things in the transfer chamber.
At least four or five will be needed.
. TOWELS, THIN CLOTH, ABOUT 3 FEET SQUARE:
Two needed for bundling everything up in the pressure cooker.
. TRANSFER CHAMBER:
Sterile chamber for sowing the seed. Described below.
. WATER DISPENSER:
For introducing water into the flasks after the seed has been sown.
Use a 2 tsp/10 ml syringe type child medicine dispenser. They are
available in most drug stores. Push a 3.5 inch piece of plastic
tubing onto the end of the dispenser to extend its reach. Tubing
can be found at most pet stores.
. WATER, DISTILLED:
For the preparation of the growth media, for washing things off in
the transfer chamber and for adding to the flasks. Must be distilled
and not just purified. Can be found at most drug stores and grocery
stores. One gallon should be plenty for 1 seed pod.
. GROWTH CHAMBER:
Orchid seed grows best if there is very little temperature fluctuation.
Since this is difficult to achieve in an open room, I keep flasks and
seedlings in an enclosed chamber with light, moisture and temperature
control. Even in these chambers, the temperature fluctuates more than
I would like, but it is better than nothing.
Each chamber is constructed from 1/2 inch plywood. They are 52 inches
wide, 24 inches high and 24 inches deep. The front is divided horizontally
into two sections. The lower of these two sections, (only about 4 inches
high) is firmly attached to the sides and bottom. The upper piece is
hinged to the lower piece, forming a door that swings down. (By the way,
this door makes a good work surface if a detachable chain is hooked to
each side to keep it in a horizontal position.) These chambers can be
stacked on top of each other, rest on a counter top or have legs added.
The inside of the chamber is water proofed by covering it with blue
plastic tarp, available in most hardware stores. A 4 foot double
fluorescent light fixture is hung inside. I use two inexpensive cool
white tubes. The light is on a timer, being on for about 14 hours a day.
A small hole in one side of the chamber, about an inch up from the bottom,
is attached to a hose to drain off excess water. I try to keep about an
inch of water standing in the bottom. The flasks and seedlings are placed
on racks just above the water.
A small fan is attached to a hole in one side to blow out the air when a
thermostat inside the chamber indicates that it is hotter than about 78
degrees. A hole in the back of the chamber is covered with a clothes dryer
louvered vent, with the louvers on the inside. When the fan is off, the
louvers close. When the fan is on, the air pressure opens the louvers and
cooler air comes in from the outside.
An automatic sprinkling system inside the chamber comes on every morning
for about 40 seconds. In my climate, (Salt Lake City, Utah) this is
sufficient daily moisture. Once a week, I do a complete watering. By the
way, short interval timers like this (40 seconds) are hard to find. If
you are electronically inclined and need to make one, contact me and I will
supply you with a schematic of mine. It uses a simple appliance timer plus
a few electronic components.
What I do not currently have in my chambers is a way to heat them in cooler
weather. I keep them in the furnace room, so I have not worried about
heating. If a person finds that heating is necessary, a submersible
aquarium heater could be used under the water in the bottom of the chamber.
However, you would probably need to increase the depth of the water and
maybe even add a float valve to keep a constant amount of water present.
. TRANSFER CHAMBER:
The transfer chamber is a box that can be sterilized, with openings in the
front to put your hands through. The top is open, and can be covered with
plastic film. Mine is made from 1/2 inch plywood, painted white with a
good quality enamel paint. It has the following dimensions:
43 inches wide
18 inches deep
13 inches high in the front
19 inches high in the back
The ends slope down from 19 inches in the back to 13 inches in the front.
Two 4 inch diameter holes are cut in the front. Their centers are located
about 12 inches in from each side.
A piece of plastic film is attached to the top back edge of the chamber.
It is big enough to come down over the top and front, covering the arm
holes, and wide enough to come down over the sides.
The transfer chamber described above is actually quite bulky and hard to
move around. I always have trouble finding a place to store it when it is
not in use. A person may want to consider making a chamber from wire frame
with good plastic film over the entire thing. A chamber could also be made,
more like the one that I have described, but that is collapsible.
. SEED FROM GREEN-POD OR MATURE-POD:
. GREEN_POD: Using uncontaminated seed from a pod that has not yet
split. My best results have been obtained from pods that are just
starting to show signs of maturing. However, once they start to
mature, they can go quickly. The flasking needs to be performed as
soon as signs of maturing show. Even waiting a day or two can result
in contaminated seed from a pod that has split open.
. MATURE-POD: Using contaminated seed from a pod that has split open.
Before the seed can be flasked, it must go through a sanitization
process. Since I have had very little success in this area, I will
not try to explain the process. See Rebecca Northen's book or the
FAQ for information.
Almost all of my flasking is done from green-pod. The only times that I
have flasked from a mature pod is if it was a cross that I was really
interested in and I didn't get to it before it split. I have had very
little success sanitizing the seed once the pod has split, and therefore,
most of this type of flasking effort has been wasted time for me.
. PREPARING THE FLASKS AND TRANSFER CHAMBER:
I always use at least 3 flasks and usually 5 per seed pod. Then, if one
or two flasks get contaminated with fungus, I still have some good flasks.
(However, many times, I end up with no contamination in any of the flasks.)
Clean the flasks and stoppers with hot water and soap. Fill the hole in
each stopper with one full cotton ball.
Mix in a 500 ml Pyrex beaker, 500 ml of distilled water and 5 teaspoons of
Moral Germinal P. While stirring, heat the solution to almost boiling in a
double boiler. While agitating the solution, divide it between the 5
flasks. (If it is not agitated whild being divided, the augur in the
solution may not be evenly distributed between the flasks, and the
solution in some flasks may not set up.) The beaker that was used to heat
the solution must be rinsed out immediately in hot water, or any solution
remaining on the sides will solidify and may be difficult to remove.
Place a stopper loosely on each of these flasks, and cover the stopper and
neck of the flask tightly with a piece of aluminum foil.
Fill two 1 quart flasks with distilled water and cover the openings and
necks tightly with aluminum foil. (Stoppers are not necessary.)
Fill the pressure cooker with about 2 inches of water. Wet a thin cloth
towel that is about 3 feet square. It must be large enough to cover
the bottom of the pressure cooker and come up the side with the four
corners hanging over the edge. Place the towel in the pressure cooker in
this manner with the 7 flasks on top of it.
Also place the following items, (all must to be wet) in the pressure cooker:
. The rest of the aluminum foil (5 pieces) in a bundle, folded in half.
. Water dispenser with a bamboo skewer pushed into the plastic tube and
broken off just a little longer than the tube. (This prevents the tube
from curling while being heated in the pressure cooker.)
. A full length bamboo skewer.
. Single edge razor blade.
. Four or five cloth towels, about 18 inches square.
Lay a second wet 3 foot square towel over the top of everything, rotated
45 deg. from the first towel. Push the corners of this second towel down
into the pressure cooker, between the first towel and the flasks.
Pull the corners of the first towel up and tie opposite corners together.
You should be able to lift the entire contents out of the pressure cooker
by grasping the first towel by the two knots and lifting up.
Place the lid on the pressure cooker and heat to 15 pounds of pressure
for 20 min. Remove from the heat, and allow to slowly cool, (for about an
hour). If you don't wait long enough, the contents of the pressure cooker
will be too hot to move to the transfer chamber. If you wait too long,
the growth media will solidify while the flasks are standing up. It must
solidify while the flasks are on their sides.
While waiting for the pressure cooker to cool, prepare the transfer chamber.
Mix up a 10% Clorox solution. I mix one 500 ml flask of Clorox to nine
500 ml flasks of tap water in a rubber bucket. Clean your hands, arms and a
spray bottle in this solution and fill the bottle with the solution.
Thoroughly spray the inside of the transfer chamber. Soak a large towel in
the Clorox solution and place it on the bottom of the chamber. Pull the
plastic film down over the top of the chamber, and with your hand through
the front holes, again thoroughly spray the inside of the chamber,
including the plastic film. Get plenty of the solution in the air inside
the chamber. Remove your arms from the chamber, leaving the spray bottle
inside, and make sure that the plastic comes down over the holes in the
front. Wash the Clorox solution off of your skin.
When the pressure cooker has sufficiently cooled, (It must still be quite
hot, but the pressure must be down), pull the plastic film back from the
left part of the transfer chamber. Open the pressure cooker and quickly
place its contents into the back left section of the chamber. (The bundle
will be HOT, and you may need to use a hot pad. If so, it should be
sterilized in the Clorox solution.) Quickly pull the plastic film back
down over the front of the chamber.
Immediately, clean your hands and arms with the Clorox solution and while
reaching through the openings in the front of the chamber, again spray the
inside of the chamber and its contents with the Clorox solution. Carefully
untie the bundle that was just removed from the pressure cooker and remove
each of the five flasks that contain growth media. (They will be HOT, and
you may again need to use a sterilized hot pad.) Try to not expose any of
the other items in the bundle to the air. Lay the five flasks on their
sides in the back right section of the chamber and cover them with one of
the smaller towels from the bundle. Again spray the entire inside of the
chamber with the Clorox solution. Remove your arms from the chamber,
again making sure that the plastic comes down over the holes and wash the
Clorox solution from your skin.
The contents of the chamber must now be left to cool. This usually takes
4 to 5 hours. Check it now and then by feeling how warm the flasks of
water are. Make sure that you clean your hand and arm with the Clorox
solution before checking the flasks. When the flasks are only comfortably
warm, it is time to sow the seed.
. SOWING THE SEED:
Remove the seed pod from the parent plant with a section of stem attached.
If the sepals, petals and/or lip are still attached, remove them, being
careful not to cut into the interior of the pod.
Thoroughly clean the pod with a toothbrush and the Clorox solution. Pay
particular attention to the groves in the pod and to the flower end. Wrap
the pod in a small piece of paper towel that has been saturated in the
Clorox solution and place it into the transfer chamber.
Thoroughly clean your hands and arms with the Clorox solution and insert
them through the holes in the front. Again thoroughly spray the inside of
the chamber with the Clorox solution.
Remove one of the flasks that contain water from the bundle of material.
Break open the aluminum foil around the top, and pour water on both hands
to clean off the Clorox solution. Remove one of the smaller towels from
the bundle and wipe off your hands. Remove another towel from the bundle
and lay it out, somewhat bunched up in the center-front of the chamber.
Remove the seed pod from the paper towel and rinse it off with the water
from the flask. Place it within the folds of the towel that is laid out
in the center-front of the chamber.
At this point, as items are used, they should be exposed to the air as
little as possible and quickly placed within the folds of this towel when
not in use. Keep in mind that this towel is resting on the bottom towel
which is saturated in the Clorox solution. You do not want the Clorox
solution to soak up into this towel and contaminate items with Clorox.
If necessary, place a second towel, bunched up under the first towel.
Remove the razor blade, water dispenser and bamboo skewer from the bundle
and cover them with the folds of the towel in the center-front of the
chamber.
In the following steps, it is important to keep the flasks in a stable,
horizontal position. Try to not disturb the growth media inside the flasks.
Move one of the flasks that contain growth media from under its towel to
the center of the chamber, placing it with its mouth to the right if you
are right handed. Wipe the top surface off with a clean towel and quickly
place the seed pod on this surface. Use the razor blade to cut off the
two ends, cutting far enough into the pod to expose a little of the white
cotton like material inside the pod. Also make three lateral cuts evenly
spaced along the sides of the pod, cutting it into three long pieces. As
these three pieces are separated, they should expose the inner cotton like
material which contains the seed. Keep these three pieces of the pod
together and again place them within the folds of the towel. Be careful
to not expose the inner material to the towel, which could be contaminated
with the Clorox solution.
Remove the stopper along with its aluminum foil from the flask in the
center, and set it aside. Make sure that the exposed end of the stopper
is not setting up or it could become contaminated. Also, make sure that
it is not pressing down against the bottom towel, which could contaminate
it with Clorox.
Use the bamboo skewer to remove a VERY SMALL amount of the inner material
from the seed pod, and carefully insert it into the flask. Wipe it around
on the surface of the growth media and again quickly cover the skewer and
seed pod in the towel. (There is a real tendency to put too much seed in
the flask. Too much will result in pore growth and must be avoided. There
should be no more then a speck of the material from the seed pod on the
end of the skewer.) It is recommended that material be taken from different
parts of the pod for the different flasks. This is because the fertility of
the seed may be different in different locations in the pod. The seed at
the flower end of the pod has the best chance of being fertile.
Use the water dispenser (with the section of bamboo skewer removed from
the plastic tube) to add water to the flask. I usually use three full
dispensers, (30 ml of water) per flask. Remove the stopper from its
aluminum foil and quickly but carefully insert it firmly into the flask.
It is not necessary to cover the stopper with a new piece of foil at this
point.
Leave this flask where it is and following the same procedures with the
other four flasks, using the first flask as an elevated surface to set
the rest of the flasks on as you work. Be extremely careful to not knock
the top flask off of the bottom flask as you work.
When you have finished with all 5 flasks, remove the plastic film from
the top of the transfer chamber. You can now use the aluminum foil to
cover the stopper and neck of the flasks. Take the foil pieces one at
a time off of the bundle of foil, and put the surface that has had the
least exposure to the air against the stopper.
. CLEAN UP:
Immediately wash the Clorox solution off of your skin and wash all towels
in plenty of water. The Clorox solution will destroy the cloth if it is
not washed out.
. IDENTIFICATION:
Dry the top surface of each flask and mark them with any identifying
information. Some permanent markers will work on the glass, or a grease
pencil can be used. I keep track of the date that the cross was made,
the parents in the cross (including an indication of which one was the
pod parent) and the date that the seed was sown.
. FLASK MAINTENANCE:
Keep the flasks in an environment that has little temperature fluctuation.
I use the growth chamber for this.
After a time, some of the growth media may turn dark. I believe that this
is from waste product build up from the growing protocorms. It can be
ignored as long as the protocorms are growing well. If a flask is
contaminated with fungus spores, the fungus will usually start to show
within two or three days. This may be seen as clumps of growth, a clouding
of the water or colored streaks in the water or on the growth media. Any
flasks contaminated with fungus must be discarded.
For Phalaenopsis, you may be able to see very small green protocorms
within two to three weeks. They should be definitely showing within 4 to
6 weeks. There will be a good layer of water above the growth media, and
you will be able to see the little protocorms in the water or on the media
if you look through the water, parallel to the surface of the media.
Since there is a lot of water in the flasks, I believe that it helps with
gas exchange to slightly move the flasks each day.
It may take 6 months or even a year to get plants of much size, depending
on how many there are in the flasks and the environmental conditions. I
would let them grow in the flask for as long as they seem to be doing well.
Once they show any sign of problems, or retarded growth, it is time to pot
them out if they are big enough, or replate them to new flasks.
. REPLATTING:
Replatting is a little tricky with the home made equipment, but it can
be done. The trick is to not pickup contamination in the process. The
procedure is basically to remove a few plants at a time from the mother
flask and place them in new flasks.
The flasks and transfer chamber are prepared in the same way as you would
for sowing seed. When everything has cooled, remove the foil from the
mother flask, (outside of the transfer chamber) and thoroughly clean the
flask and stopper with the 10% Clorox solution. Be sure to use the
toothbrush around the union of the stopper with the glass. Clean your
hands and arms with the solution and place the flask of seedlings inside
the transfer chamber. Use the water that you have sterilized to clean
your hands and thoroughly clean the flask and stopper.
The transferring of the seedlings to new flasks is basically the same as
sowing the seed. Remove the stopper from the mother flask and wipe the
inside portion of the neck with a clean sterile cloth. Reach inside the
flask with a long spoon or other object that you have sterilize in the
pressure cooker. Scoop out some of the seedlings and insert them into
the new flask, which should be setting on top of the mother flask. Add
water as you would for seed sowing and insert the new flask's stopper.
After replatting all of the flasks, I usually just leave what is left in
the old flask, add new water and close it up with a new stopper. What
remains may continue to grow.
If any of the flasks get contaminated during this process, all that you
can do is remove the seedlings, pot them up and hope for the best.
. ADDING WATER TO A FLASK:
If your environment is too dry, the flasks may dry out before they are
ready for potting out or replatting. If this happens, sterile water must
be added to the flask. Follow the same procedures as you would for
replatting, but don't remove the seedlings from the flask. Just add water
that you have sterilized in the pressure cooker.
. POTTING OUT:
I will assume that you are familiar with potting seedlings out from the
flasks. Rebecca Northen covers this in her book.
. STEM PROPAGATIONS:
The procedure for sowing seed can also be modified for stem propagations
of Phalaenopsis orchids. There is an article about the process in the
January 1966 AOS bulletin. I recommend that you contact the AOS and get
a copy of the article. The procedure is as follows:
Cut the flower stock into sections containing one dormant bud per section.
There should be about 1.25 inches of step below the bud and about .75
inches of stem above the bud.
The trick now is to get these stem sections sanitized without killing the
bud. Use a razor blade to carefully remove the sheath that covers the bud.
Scrape away as much of the material as you can without damaging the bud.
Sanitize these stem cuttings in hydrogen peroxide plus a little dish soap
for about 1/2 hour, agitating the solution now and then. Move them to a 10%
Clorox solution for 15 minutes, again agitating the solution now and then.
The rest of the procedure is like sowing seed. Put the stem cuttings in
the transfer chamber and wash them off with sterile water. Cut off about
.5 inch of the stem below the bud (the longer stem) giving a new clean
cut on this end. Using long sterile tweezers, insert the cuttings into the
growth media up to the bud. Add water and seal the flask with a stopper
and foil. I normally use large test tubes in place of the quart flasks for
this process. Keep the flasks of stem cuttings in the same location as the
flasks of seedlings.
Since it is difficult to get all of the cuttings completely sanitized,
you should only put one cutting in each flask or you stand the chance
of contaminating everything.
If all goes well, the bud should start to swell and within a few weeks
it should start to form a new plant. Pot it out when it has developed
good roots.
Since it is very difficult to get the stems completely sanitized, there
is a high chance of getting contamination in the flasks. If this happens
and is caught soon enough, the stems can be removed, resanitized and
placed in new flasks.
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Addenda:
Timing circuit, as mentioned above.
From ddixon@ES.COM Thu Nov 21 16:54:58 1996
To: ahicks@nmt.edu
Subject: Short Interval Timer Circuit
Hi Aaron,
A while back you added an article that I wrote on "flasking with home-made
equipment" to your FAQ under flasking.stem-prop. In that article, I mention
a 40 second timer circuit. A number of people have contacted me to get the
circuit description, so I thought you might also want to add it to your FAQ.
Feel free to use it if you would like.
Darrell (ddixon@es.com)
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40 SECOND TIMER CIRCUIT
21 November, 1996
Darrell K. Dixon
email: ddixon@es.com
INTRODUCTION:
The conditions under which I grow my orchid seedlings, require a short
daily misting. Since commercially available short interval timers are
hard to find, I designed the following timer circuit. Building it
requires a minimal knowledge of electronic circuitry and components.
CIRCUIT DESCRIPTION:
The circuit is built abound a 555 type timer chip. When power is initially
applied to the circuit, the output from the chip goes high for the time
interval specified by the RC network, (which I have set to about 40 sec).
After this interval, the output goes low and stays low until power is
removed from the circuit and re-applied. The output from the circuit
drives a relay which drives a solenoid valve. Power to the circuit is
supplied by an ordinary appliance timer, like the ones that plug into the
wall with a lamp plugged into them.
So, when the appliance timer applies power to the timer circuit, the timer
circuit applies power to the relay which activates the solenoid valve. The
timer circuit removes power from the relay after the time period specified
by the RC network, even though the appliance timer is still applying power
to the circuit.
The appliance timer could have multiple on/off settings so that watering
could be done at multiple times during the day.
PARTS LIST:
. Capacitor, C1 (6.5 microfarads):
The capacitance part of the RC network.
. Diode, D1 (1N4003):
Prevents the relay coil's back-EMF from damaging transistor T1.
. Power Supply, 12 volts DC:
This power supply plugs into the appliance timer and provides Vcc+ for
the circuit.
. Relay, 12 volt DC coil:
Drives the solenoid valve.
. Resistor, R1 (6.2 megohms):
The resistance part of the RC network.
. Resistor, R2 (2.2 K-ohms):
Input to the gate of transistor T1.
. Timer, Appliance type:
Applies power to the 12 volt DC power supply.
. Timer Chip, 555 type:
This is the heart of the timer circuit.
. Transistor, T1 (2N3053):
Drives the relay.
TIME PERIOD:
The time period of the circuit in seconds is approximately equal to the
product of R1 in megohms and C1 in microfarads. Hence, for the values
specified: 6.2 x 6.5 = 40.3 seconds.
CIRCUIT LAYOUT:
. CAPACITOR C1:
Connect the positive side of C1 to one lead of R1. Connect the
negative side of C1 to ground.
. DIODE D1:
Connect the two leads of D1 to the two leads of the relay coil.
(Putting D1 in parallel with the coil.) Connect the cathode lead
of D1 to Vcc+. Connect the anode lead of D1 to the drain of T1.
With the cathode end of D1 connected to Vcc+, you may think that
D1 is connected incorrectly. It is not. The purpose of D1 is to short
out the relay coil when power is removed from the coil, thus preventing
the coil's back-EMF from damaging T1.
. RELAY:
The coil leads are already connected to the two leads of D1.
. RESISTOR R1:
One lead of R1 is already connected to the positive side of C1.
Connect the other lead of R1 to Vcc+.
. RESISTOR R2:
Connect one lead of R2 to pin 3 of the timer chip. Connect the
other lead of R2 to the gate of T1.
. TIMER CHIP:
. Pin 1: Connect to ground.
. Pin 2: Connect to pin 6 and to the junction between C1 and R1.
. Pin 3: Already connected to one lead of R2.
. Pin 4: Connect to Vcc+.
. Pin 5: Not used.
. Pin 6: Already connected to pin 2.
. Pin 7: not used.
. Pin 8: Connect to Vcc+
. TRANSISTOR T1:
. Source: Connect to ground.
. Gate: Already connected to one lead of R2.
. Drain: Already connected to the anode side of D1.
CONNECTING A SOLENOID VALVE TO THE CIRCUIT:
To drive a solenoid valve with the circuit, simply use the relay contacts
as a switch for the solenoid valve's power supply.
COMBINING THE SOLENOID VALVE'S POWER SUPPLY AND THE 12 VOLT DC POWER SUPPLY
Instead of driving a 12 volt DC power supply with the appliance timer,
drive a transformer that has an output voltage equal to what the solenoid
valve needs. The output from this transformer goes two places: through the
relay contacts to drive the solenoid valve, and to a 12 volt DC power
supply circuit. This power supply circuit is simply a full wave bridge
rectifier chip, a 12 volt regulator chip and a filter capacitor. Vcc+ is
the output from this power supply circuit.
CASCADING TIMER CIRCUITS:
I believe that multiple timer circuit, each with its own relay, could be
cascaded. This way, as one turns off, the next one would turn on. This
would be the way to drive multiple solenoid valves if water pressure is a
problem.
To cascade the circuits, I would use a DPDT relay. One output from the
relay would drive the solenoid valve. The second output from the relay
would drive the next timing circuit. This second output would get its
power directly from the 12 volt DC power supply. Its contacts would be
open when the first output was driving the solenoid valve and then closed
when the circuit's RC time constant had expired, thus enabling the next
timer circuit.
MAKING A VARIABLE TIME PERIOD:
To make the time period of the circuit variable, use some type of variable
resistor in the RC network.
LONGER TIME PERIODS:
Since the time period is determined by the resistor and capacitor from
the RC network, larger values will give longer periods of time. However,
there is a limit to how large these values can be and still have the
circuit function dependably. Also, you will probably have trouble finding
components that will give a very long time period. Anything much over 90
seconds is probably beyond the capacity of this circuit.
There are other circuits and timer chips that will give longer periods of
time. Books are available that cover these other chips and circuits. Look
specifically for books on TIMERS and TIMER CIRCUITS.
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