generating pulse

Cheapest is a microcontroller running on its internal RC oscillator, which you may have more or less calibrated.

If you don't want to use microcontrollers, you can use a 1 Hz oscillator that feeds a monostable that generates 50 ms wide, high logic-level pulses. A second monostable is set to trigger on the high-to-low transitions of the first monostable's output, and also generates 50 ms wide, high logic-level pulses. You can do the whole thing with a 40106 (hex inverter with schmitt-trigger), three capacitors, three resistors and two diodes, as shown in the figure.

http://80.35.195.131/ng/ng_20060623A01.png

R1 & C1 such that period is 1 s. R2 & C2 such that A and B pulses are 50 ms wide. D1 can be 1N4148.

Best,

So, you want: ___ Trig ___| . . . (doesn't matter?) __________ A ___| |________________ . . . (until next trigger) __________ B ______________| |_____ . . .

???

You can do that with two of these.

Tim

-- Deep Fryer: a very philosophical monk. Website:

_ _ _ _ | | | | | | | |

-- -- --------------------- -- --- T 0 1 2 3 Repeat

So you want T0-T1 = 50 mS, T1-T2 = 50mS, T0-Repeat = 1000 mS?

Count to 20 in 50 mS steps (drive 4017's with a 555 running at 20 hZ, set the 4017 chain to reset at count 20). Use counter output 0 and

Ed