Rain Detector Circuit

This circuit uses a sensor made of a small piece of etched PC board and a simple SCR circuit to detect rain and sound a buzzer. The SCR could also be used to activate a relay, turn on a lamp, or send a signal to a security system.

Part	Total Qty.	Description	Substitutions
R1	1	1K 1/4 W Resistor
R2	1	680 Ohm 1/4 W Resistor
D1	1	1N4001 Silicon Diode
BZ1	1	12V Buzzer
S1	1	SPST Switch
SCR1	1	C106B1 SCR	106CY
SENSOR	1	See Notes
MISC	1	Board, Wire, Case, PC Board (For Sensor)

NOTE:

1. The sensor is a small piece of PC board etched to the pattern showen in the schematic. The traces should be very close to each other, but never touching. A large spiral pattern would also work.
2. Make sure to use a loud buzzer.

7 Segment LED Counter

This simple counter can be used to count pulses, as the basis for a customer counter (like you see at the doors of some stores), or for anything else that may be counted. The circuit accepts any TTL compatible logic signal, and can be expanded easily.





R1-R7----470 Ohm 1/4 Watt Resistor
U1------- 74HC90
U2------- 74HC47
Disp---- 7 Seg Common Anode


NOTE:

1. All pulses to be counted are to be TTL compatible. They should not exeed 5V and not fall below ground.
2. You can add more digits by building a second (or third, or fourth, etc...) circuit and connecting the pin 11-6 junction of the 74LS90 and 74LS47 to pin 14 of the 74LS90 in the other circuit. You can keep expanding this way to as many digits as you want.