Can a old-fashioned Germanium Diode be used with a 555 to drive a 4017, or drive a 4017 alone??

Thread Starter

Kim Sleep

Joined Nov 6, 2014
38
Can a old-fashioned Germanium Diode be used with a 555 to drive a 4017, or drive a 4017 alone?

I was able to do it once before, and now, no matter what can not do it again.
What I got before was a nice, really slow, rather "random" triggering of the 4017.
But now, I can no longer seem o do it, and Ive backed myself into a corner, as Im supposed to recreate it again.
Thanks for any help you may have.
I have now attached the schematic. Diode used is an Oa7
 

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MrChips

Joined Oct 2, 2009
30,488
I assume that you are trying to build a random noise generator.
There are random noise circuits using reversed biased PN junction devices. You will have to amplify the signal to make it trigger logic circuits.

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PE July 1971 Drummer Boy noise generator.jpg
 

MrChips

Joined Oct 2, 2009
30,488
What does it take for a signal to drive a CMOS logic circuit?
Not much. All you need is the signal to exceed the lower and upper switching threshold voltages.

For CMOS gates, the threshold is just below and above Vdd/2.
 

Dodgydave

Joined Jun 22, 2012
11,240
Yes, but i would also put a 100 ohms resistor in series with the diode as well , because when the chip discharges the capacitor the voltage across it may blow the diode.
 

AnalogKid

Joined Aug 1, 2013
10,944
Looking at #13, it looks like the C2 charging current is the approx. 1.3 uA. This is a reasonable leakage current value for a germanium diode. I have one old datasheet that lists the 1N34 reverse current as "30 uA @ 10 V". Does it vary enough with temperature, etc. to be a source of randomness? Don't know, but probably not.

To the TS - what is it you are trying to achieve?

What is the goal for the overall circuit?

Do you think you need a random-frequency clock source?

If so, why?

ak
 
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eetech00

Joined Jun 8, 2013
3,823
Can a old-fashioned Germanium Diode be used with a 555 to drive a 4017, or drive a 4017 alone?
The 4017 has restrictions on the characteristics of the clock signal. The signal must meet these restrictions to reliably trigger the 4017. Basically, the signal needs to be as "square" as possible with sharp edges. The 555 in your diagram conditions the randomized signal so it can reliable trigger the 4017 in a somewhat random fashion.
 
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