A quick circuit check

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Hi Freaks,

here is a small circuit I've just designed to see if I could do it without a µC.

It is supposed to put a 1 to Q0 after the button is pushed for the first time. A second push will shift the 1 to Q1 and leave all other outputs zero etc. After the one reaches Q7 the next push will start the cycle again. (starting with Q0 being 1)

Is my idea with the cap and two resistors good? They are supposed to handle MR. Can you spot any flaws in my design, besides not including a micro?

PS: R1 is connected to Vcc.

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Do you need the 10k resistor at all? Usually you'll just see a resistor to V+, cap to GND and the junction to reset. But if you want the resistor, I think your ratio is not high enough. The reset line will only go to 2/3Vcc, which is pretty marginal. I think you'll want to make the 10k resistor a fair deal larger. If you have a spare Schmitt trigger inverter you could also use that to square up the reset. In that case you'd need to reverse the resistor and capacitor (r to GND, c to V+).

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So you need to have 8 outputs, all at zero, and when button is pushed, first input only goes on, and when buttons are pushed more, only the next input goes on?

It might be easier with other chips, like 4017 decade counter? Just limit the count to what you need by connecting first unneeded output to reset.

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One more thought. You could replace all the data-in gates with a single R-S flip flop. Set it on reset, clear it when a 1 appears on Q0, and set it when a 1 appears on Q7.

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Have you ever heard of a 4017 chip?

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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js wrote:
Have you ever heard of a 4017 chip?

If he read my post, yes he has :)

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:oops: but I didn't. That chip was used in many designs in my younger days. :)

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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thanks for all the ideas :)

Quote:
Do you need the 10k resistor at all?

I'm not sure. What happens if turn the thingy off and quickly on again? My bet is, that my 164 will get random output stages while the cap is still loaded, so I don't get a reset. (Yeah, I need another ratio ... it's a voltage divider after all ^^)

@js: yupp, jepael just told me ^^ :D

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Nephazz wrote:
thanks for all the ideas :)

Quote:
Do you need the 10k resistor at all?

I'm not sure. What happens if turn the thingy off and quickly on again? My bet is, that my 164 will get random output stages while the cap is still loaded, so I don't get a reset. (Yeah, I need another ratio ... it's a voltage divider after all ^^)

Depends on what OFF means. :)

Usually there are many current paths from Vcc to GND which will let the capacitor discharge back through the 4.7k resistor. You can speed up that process even more by wiring a diode across the resistor, anode to capacitor and cathode to Vcc.