What a dingus! - CD4024BE

ive got one of these in my modular which is a key to almost every pathc i make.

i was just hunting about for schematics cos im about to stick one into my 80s yamaha pc100 keyboard to divide down the main clock. its all internal so i dont need as much buffering to the outside which is nice.

i dont need reset either but i just want to know: what the hell is up with that crazy reset circuitry?

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I really canā€™t explain that sorry, but surely someone else here :slight_smile:

If i remember correctly the logic high levels are dependent on the supply voltage.

My guess is the reset circuitry is there to accommodate for gate voltages lower than Vdd.
Itā€™s just two cascaded inverting stages, biased by the the other transistor.

Also the rise time will be faster with higher input levels

I have no idea whatā€™s up with that bias circuit, I havenā€™t seen anything like it before.

Hereā€™s another 4024 based divider whose reset input is conditioned by two transistor stages, but without any such bias circuit.

~~http://www.modular.fonik.de/pdf/SimpleDividerSCH.pdf~~

(Does it really need four diodes for reset though?)

Never mind, I went back and looked at Rƶnnbergā€™s page (Niklas Rļæ½nnberg's homepage - Audio DIY) and it says

Itā€™s original design was made by Mathias Herrmann for his inspiring Fonitronik. However, his design gives inverted outputs, which I changed to normalized outputs. Also I added a start-up reset pulse, to ensure that all outputs are low when the modular is started.

So the ā€œbias circuitā€ is actually that startup pulse: When power is applied, the center left transistor turns on and kicks the reset input. The rest is a pair of inverting buffers to condition the input pulses, as said.

Fonitronikā€™s design: http://www.modular.fonik.de/pdf/SimpleDividerSCH.pdf

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Oh wow thatā€™s pretty cool, i didnā€™t think of it but it makes sense because itā€™s an npn that would go low when the capacitor on the base charges.

In fact, itā€™s so clever it might be worth adding to a lot of other circuits :slight_smile:

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Nice. I also get that and like tge benefit in some circumstances. I tried to look it up but it was down when I went thereā€¦

Rƶnnbergā€™s site looks to be permanently dead; above I linked to an Internet Archive copy.

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