THERE IS AN UPDATED VERSION OF THIS PROJECT USING AN EASIER TO WIRE AND PROGRAM CONTROL MODULE AVAILABLE HERE.

This project is to assemble a very inexpensive controller capable of executing the frequent, short duration valve controls required for mist bed plant propagation. It requires only a few dollars worth of parts which are readily available on Amazon.com and simple wiring. While it is not as full functioned as some commercial mist controllers, it cost about 20% of what even the least expensive controllers retail for and is a good start for someone just wanting to experiment.

Please keep in mind that any project that involves electronic devices carries some risk and this is doubly true when the project also involves water. Please use caution and be sensible if you build this or any other electronic device.

The scope of this instructable is only the timer circuit and does not cover the other materials needed to have a fully functioning mist propagation bed. There are plenty of resources out there with information about types of mist nozzles and how to plumb them. This instructable covers only how to make the valve open and close with the required timing.

The entire control circuit including the valve is less than $30 (assuming you are a Prime member) while the least expensive commercially produced mist timers I was able to locate start at about $90 and they do not include the valve so you are looking at over $100 on just the control circuit.

Step 1: Materials and Tools

The materials needed are all available from Amazon.com as well as probably many other sellers.

MATERIALS:

• A 12 volt DC, 2 Amp power supply (with terminal block adapter for easier wiring)

• A programmable time delayed relay Be sure to select the YYC-2 12 volt model.

EDIT: It has been brought to my attention that this part is no longer available from the original Amazon link. It can still be found on Ebay if you search for "12V Timed Relay Module"Here is an example of one seller

EDIT 2: I found another slightly more expensive Amazon seller as wellHERE

• An irrigation solenoid valve

• You will also need some wire which you can probably find laying around. Anything from 14 down to 22ga. should be fine.

TOOLS:

• Wire strippers

• A small screwdriver (for the terminal blocks of the relay and power supply)

Step 2: Hooking It Up...

The wiring is quite simple but it is important that you attach the wires correctly or damage to the equipment can occur.

Note: On each end of the timer relay there are 3 terminal blocks. On the input side, the unused terminal is for a trigger signal which we will not be using in this application as we want the timer to cycle continuously. On the relay side the extra terminal is the "normally closed" pin off the relay and would cause our timing to be the opposite of what we desire (a short run time followed by a long pause). Both these terminals should be left empty.

Begin by determining which is the positive and negative output of the terminal block. They should be marked with a plus sign and a minus sign.

1) WHILE UNPLUGGED FROM THE WALL attach a piece of wire from the "+" terminal on the power supply to the VCC terminal on the timer relay board. This is marked on the back of the board but it is the top terminal closest to the number display.

2) Attach a second small piece of wire from that same terminal on the timer/relay around to the center terminal (labeled "COM" on the back of the circuit board) on the relay side.

3) Connect a wire from the bottom terminal (labeled "CK" on the back of the circuit board) to one of the wires of your irrigation valve. (either wire should work).

4) Connect the other wire coming off the solenoid valve to a wire which connects to the bottom terminal on the timer side of the timer/relay board (Labeled GND on the back of the circuit board).

5) Finally, complete the circuit by attaching a second wire to the GND terminal on the timer side of the relay and connect it to the "-" terminal on the power supply.

6) Make sure all connections are secure and there are no lose or exposed wires which could cause a short.

7) Plug in the power supply and the timer module should light up. If it didn't, unplug and check your wiring. If it lit up- time to program the timer.

Step 3: Programming the Timer

If there is one down side to this inexpensive timer/relay module it is the lack of clear instructions. I will do my best to help you here, but honestly, expect to spend a few minutes pushing buttons and messing things up before you get the timing and relay actuation set how you actually want it. I promise, it can be done!

First, here is the full timer instructions translated by someone else from Chinese to Russian and then by me (va an automated online translator) into English. Below that I will try to offer up clearer directions on what we are trying to do.

Stopping at any angle and at any time can be done forcibly, using the power off buttons of the electric. engine. Digital time relay. Model YYC-2 Specifications: Operating voltage: 10 ~ 16V Voltage Signal: 4 ~ 20V DC Time range: 0.1 ~ 99.9 seconds; 1 ~ 999 seconds; 1 ~ 999 minutes Output Power: DC 30V 10A or AC 220V 10A Static Current: 20mA Operating Current (Relay On): 50mA Operating Temperature: -40 ~ 85 ° C PRINTING CAPACITY: 64 * 35 * 18mm Weight: 25 d Button assignment K1 - Selects the timer mode. P1, P2, P3, P4. K2 - Enable and / or toggle the setting of the timer registers. 1st, 2nd, 3rd. The adjustable register flashes. When K3 is pressed, the value of the adjustable register is increased by 1 unit. To go to the next register, press K2 once. K3 - Selects the value of 1/10 seconds, seconds or minutes. 00.3 - 3/10 seconds. When the time counts, the point does not blink. 07.0 - 7 seconds. When the time counts, the point does not blink. 90.0 - 90 seconds. At the time counting, the tenths are displayed. 003 - 3 seconds 070 - 70 seconds. (1 minute 10 seconds). 900 - 900 seconds. 003. - 3 minutes. When the time counts, the point flashes. 070. - 70 minutes. (1 hour 10 minutes). When the time counts, the point flashes. 900.-900 minutes. (15 hours 00 minutes). When the time counts, the point flashes. The "clock" setting is carried out in the translation of the time in minutes. Max 999 minutes = 16h. 39m. Timer modes. To select a mode, press K1 for two seconds. The display shows the mode number. To select the next mode number, press K2 again. For each mode, the time settings are individual and stored in the timer memory. Mode P-1. In this mode, one time interval is set. To adjust the time, press K2 once. The timer waits for the control signal to appear on the IN terminal. When it appears, the time starts. At the same time, the relay is switched on, and after the set time has elapsed, it will turn off. When a second control signal appears, when the timer has not yet worked, the relay turns off and the counter is reset to the set time. Mode P-2. In this mode, two time slots are defined. To adjust the time, press K2 once. The first time interval is set-the delay time before the relay is turned on, after the control signal has arrived at the IN terminal. The blue LED does not light up. After setting the first time interval, press K2 once and set the second time interval - the time that the relay will be in the on state. At the same time, the blue LED is on. After setting the time, the registers do not blink. Switching the range of 1/10 seconds, seconds or minutes is done by the K3 button simultaneously for both time slots. The timer waits for the control signal to appear on the IN terminal. When it appears, the time delay starts, then the relay activation time starts. Mode P-3. Cyclical. In this mode, two time slots are defined. To adjust the time, press K2 once. First, the first time interval is set - the time when the relay is on (the blue LED is on), and then the second - the time when the relay is off (the LED is off). Switching the range of 1/10 seconds, seconds or minutes is carried out simultaneously for both time slots. The timer will cyclically (alternately) turn the relay on and off in the specified time interval. The trigger signal on the IN terminal has no effect on the operation of the timer. The button K1 can independently change the status of the relay to the opposite. Mode P-4. In this mode, one time interval is set. To adjust the time, press K2 once. The timer waits for the control signal to appear on the IN terminal. When it appears, the relay will turn on and the timer will wait when the control signal disappears. The relay is on, the LED is on. Then the timer will work out the set time will turn off the relay. If the timer did not work, but a control signal appeared on the IN terminal, the counter is reset to the set time and waits for the signal on the IN pin to be lost. To adjust the time, press K2 once. The timer waits for the control signal to appear on the IN terminal. When it appears, the relay will turn on and the timer will wait when the control signal disappears. The relay is on, the LED is on. Then the timer will work out the set time will turn off the relay. If the timer did not work, but a control signal appeared on the IN terminal, the counter is reset to the set time and waits for the signal on the IN pin to be lost. To adjust the time, press K2 once. The timer waits for the control signal to appear on the IN terminal. When it appears, the relay will turn on and the timer will wait when the control signal disappears. The relay is on, the LED is on. Then the timer will work out the set time will turn off the relay. If the timer did not work, but a control signal appeared on the IN terminal, the counter is reset to the set time and waits for the signal on the IN pin to be lost.

Now that we have that out of the way, why don't we whittle that dense block of text down to just the important stuff you need to know:

• When you hear a click and the blue LED comes on, that means the relay is engaged and if you wired everything correctly, your valve will be open.

• The left-most button scrolls through the 4 functions of the device. (press and hold for 2 seconds to toggle between them) For our application we need P-3 because it will cycle endlessly without need for an external trigger. Press and hold the left-most button then tap it until P-3 is displayed.

• Chances are that your timer came from the factory set to tenths of a second and we want to use seconds. The right-most button is used to change the unit of measure (tenths of a second, seconds, or minutes) Whatever unit is chosen will be the same for T1 and T2 (the times on and off respectively.)

• Once you get it set to seconds and use the center button to program for your desired times. (600 seconds = 10 minutes which is where I started but you can use whatever suits your application)

• Once you get things programmed, you should hear the "click" from the relay (blue boxy thing on the circuit board) as well as the click from the solenoid on the irrigation valve, the blue LED should be on, and the display should be counting down from your programmed time. When the countdown reaches 0, you may hear another click, the blue LED will go off, and the countdown should start at your "off" time in our case 600 seconds. When this countdown reaches 0, you should again hear the clicks, see the blue LED, and the countdown will again display your "on" time. This will repeat until power is removed.

• The circuit does remember the set programming when unplugged so if you do not wish to mist round the clock, just plug the power supply into a generic lamp timer set for the hours you want it to run.

• Depending on your application, you may need to adjust the timing dramatically from the example parameters I have given here.

Step 4: 12 Vs. 24 Volts and AC Vs. DC

Most irrigation valves are actually designed to run on 24 volts AC, while this setup has the valve operating on only 12 volts of DC current. There is a great article HERE about the electrical engineering behind how and why this works.

Good luck. I hope this was helpful. Please feel free to post (constructive) questions or comments below.

Happy Propagating!