Help! Where Are My Sprinkler Valves Located?

One summer after I had moved into my new house I found that the sprinkler system didn't work correctly. I noticed that when the water was not on the sprinkler heads still leaked water. I figured that the values were probably dirty and were not closing properly. So I set out one morning to bleed the values and clean them up as necessary. The only problem is I had no idea where the valves were located. I knew they were under the ground somewhere in my yard. I looked and looked but could not find them. I used a metal detector, probed the ground, everything. Then I had an idea about building the following circuit.

The valves make a clicking noise when their solenoids open and close the water valve. I figured that if I turn the valves on and off (after turning off the water supply) and listen then I might be able to hear the valves operating. The problem is that I didn't have anybody that would stand around flipping the switch on/off while I walked around the yard listening. So I built this circuit and connected it to the sprinkler system. Within two minutes I found the valves and had the leaks all fixed.

Parts List: wire, (AA,AAA,C,D or 9V) batteries, toggle switch, relay, leds, NTE955 timer chip, 1k resistors, 5k resitors, 4k resistor, 100uF capacitor, battery clip or battery pack holder, circuit board.

The tools used for this project are as follows:
Digital Multimeter
Soldering Iron
Solder
Soldering Flux
Magnifying Glass
Wire Cutters
Wire Stripper

The wiring schematic is shown in the picture.

Usage Instructions:
1. turn off water to sprinkler system
2. connect valve across relay (24VAC systems)
3. turn on circuit by closing SPST switch
4. turn on sprinkler system and select valve that is connected to the circuit.
5. LED light on circuit will blink alternately.
6. relay will open and close one time per second.
7. sprinkler valve will turn on one time per sec.
8. listen to ground and you should hear valve turning off and on.
9. if you still can't find valve then increase timer circuit frequency by changing values of R1,R2 and C per the equations shown below. Increasing frequency will make solenoid hum louder.

Place the parts on the project board and solder the wires to each part per the schematic. Put flux on each solder joint prior to soldering.

At the control panel for you sprinkler system disconnect the wires from the switch that control the valve you are trying to locate. Insert the Sprinkler Valve Finder inline. The circuit basically is taking place of the control panel switch. Once connected turn on your sprinkler system like normal (remember to turn off the water first). Now flip the SPST toggle switch on the circuit. Your valve will not turn on and off at the same rate the LEDs on the board are flashing. Go out into your yard and start listening.