TLC556: I would like to use 1/2 of 556 as one shot to turn other 1/2 astable pulse generator on/off. Regards, Erik

Part Number: TLC556

Would like to switch astable 556B on/off by one shot 556A.  Low speeds.  Regards, Erik <email address removed>

Erik,

Connect output pin of timer A to the reset pin of timer B. Timer B will run only pulses when Timer A is high (one shot running). Timer B will normally be static output low. First A-stable high pulse will be longer because timing capacitor starts at 0V and all of the remaining pulses will start at 1/3 VDD.  Adding a PNP transistor and 2 resistors can precharge the cap to 1/3 VDD. The last pulse could be cut short if the mono stable (Timer A) goes low in the middle of the stable outputting a high pulse level.

Use TLC555 A-stable calculator tool, , to choose components for A-stable timer.

R6, T1, and R4 precharge the cap C2. Set R4 = 2 * R2 and R6 is not critical, 5 * R4 is fine.

Whole Tina circuit here, TLC556 Mono control Astable.TSC

Thank you Ron for prompt and thorough reply!

I have selected some component values ( that recommended calculator did not get through my old computer...). I ended up with the enclosed sketch.  Could anyone check it out?  I have not done any detailed design for quite a few years..

1. It does not matter if first pulse is up to 2x as long as others

2. It does not matter if last pulse is cut off

3. would like high resistance values to keep Cs down

4. The monostable output shall stay high for about 30 seconds

5. The astable must reliably start and run for that time only, producing about 6 pulses, each approx. 100 ms long, once every 5 seconds   

A. I picked following values:

R 18 M

C1 1.5 microF

R1 390 k

R2 18 M

C2 0.39 microF

D1 & D2 are 1N4148

Chip is TI TLC 556 CN, 14 DIP for prototype

What is recommended decoupling between pins 14 & 7 ?

Anything else to be corrected or completed?

Thanks to anyone in advance!

Erik VE7ZQ

Woops!

Here is the sketch I wanted to attach...

Erik