ALTERNATING ON-OFF SWITCH

ERROR FIX: The LED (Led1) was drawn up-side-down. Fixed.
Parts List
Resistors are carbon, 1/4 Watt, 5% tolerance.
R1 = 10K
R2 = 100K
R3 = 10K
R4 = 220 Ohm (optional)
C1 = 0.1μF, Ceramic (100nF)
C2 = 1μF/16V, Electrolytic
D1 = 1N4001 (see text)
Led1 = Led, 3mm, red (optional)
Q1 = 2N4401 (see text)
IC1 = 4069, CMOS, Hex Inverter (MC14069UB), or equivalent
S1 = Momentary on-switch
Ry1 = Relay (see text)
Use this circuit instead of a standard on-off switch. Switching is very gentle. Connect unused input pins to an appropriate
logic level (I used ground). Unused output pins *MUST* be left open!
First 'push' activates the relay, another 'push' de-activates the relay.
IC1, the MC14069 (or 4069) is a regular Hex-inverter type and is constructed with MOS P-channel and N-channel
enhancement mode devices in a single monolithic structure. It will operate on voltages from 3 to 18 volts, but most
applications are in the 5 to 15 volts. Although the 4069 contains protection circuitry agains damage from ESD (Electro
Static Discharge), use common sense when handling this device. Depending on your application you may want to use an
IC-socket with IC1. It makes replacement easy if the IC ever fails.
You can use any type of 1/4 watt resistors including the metal-film type.
The type for D1 in not critical, even a 1N4148 will work. But, depending on your application I would suggest a 1N4001
(or similar) as a minimum.
Any proper replacement for Q1 will work, including the european TUN's. Since Q1 is just a driver to switch the relay coil,
almost any type for the transistor will do. PN100, NTE123A, 2N3904, 2N2222, 2N4013, etc. will all work.
For C2, if you find the relay acts not fast enough, you can change it to a lower value or use a ceramic cap of around 0.1μF.
It is there as a spark-arrestor together with the diode (D1).
For the relay I used a 6 volt type with the above circuit and 9 volt battery. The circuit will work fine with 12 Volt, the only
thing to watch for is the working voltage of C2; increase that to 25V if you use a 12V supply.
I added the Led to have a visual indication of being 'on'. For use with 12V supply make R4 390 ohms. The LED and R4
are of course optional and can be left out. Your application may already have some sort of indicator and so the LED and
R4 are not needed.