Touch Switch
Touch Switch
(OP)
I am implementing a touch switch: when i touch the metal plate it triggers the 555 in the monostable mode, that goes into a 7476 (JK Flip Flop)which simple toggles, it sends the high into the relay and in turn lights up an LED connected to the normally open switch of the relay (relay: 5v - 1am). But my problem arises when I touch the metal plate again to turn off the LED. The LED turns of for a second but then turns on again, I'm thinking there is still some voltage within the coil of the relay. I placed a diode parallel to the relay coils (reversing the polarity of the diode) to avoid any voltage from going back through the coil but it doesn't seem to help much. Any help?





RE: Touch Switch
All I can suggest is that you simplify your circuit with a D type flip flop (4013) configured with the Q o/p wired back to the data input. A low going edge at the clock input driven from your touch switch circuit will clock the value on the data input to the Q output and set up the data input for your next press. You don't need a relay to drive a LED - the D type output can sink 10mA. If you need more use a transistor, lot cheaper than a relay and no horrible inductive coils to worry about.
Rgds, Boxxy
RE: Touch Switch
RE: Touch Switch
Signetics 555 timer ap note AN170 has this rather criptic
but useful statement:
"6. Double triggering of the TTL loads sometimes occurs. Why?
Answer: Due to the high current capability and fast rise and
fall times of the output, a totem-pole structure different
from the TTL classical structure was used. Near TTL threshold this output exhibits a crossover distortion which may double trigger logic. A 1000pF capacitor from the output to ground will eliminate false triggering."
Hope this helps.
Cheers,
Rich S.
RE: Touch Switch
RE: Touch Switch
Make sure you have pin 5 bypassed to ground with a
cap in the 0.1uF range. This is an internal reference
level.
Rodar
RE: Touch Switch
RE: Touch Switch
RE: Touch Switch
http://www.qprox.com/downloads/manuals/e116.pdf