How to toggle a reset pin LOW briefly when powering up

I'm building a AY-3-8910 (NES sound IC) synth

Everything is fine, except that on startup, the AY-3-8910 needs a reset pulse in order to work fine afterwards.

Right now I'm doing it manually and could do it with an Arduino pin, but I would like to save that pin for other things.

The datasheet [1] says this:

RESET (input):
For initialization/power-on purposes, applying logic “0” (ground)
to the Reset pin will reset all registers to “0”. The Reset pin is provided
with an on-chip pull-up resistor

I've read about RC filters that can make temporary 0v after getting 5v again on power up, and tried with different values but can't make it work.

Also, there is this forum [2] where a user said that could make it work like this:

I connected the Reset pin of the AY chip to pin 17 of the PicAxe and sent it a reset pulse after power up and the noise works fine on all four of my 0426 chips.

After that I connected a pullup (1.8k) resistor and a (4.7 uF) capacitor to the reset pin and that works too. Just putting a pullup resistor will not work. Apparently it wants a solid reset after power up.

But I don't really understand how he connected it, seems to me that he connected VCC through a resistor and a capacitor to RESET, but that does nothing. Also it seems weird to me he connected it to VCC because on the datasheet it says that it has a internal pullup resistor.

Thanks!!

REFERENCE:
[1] AY-3-8910 datasheet:
http://f.rdw.se/AY-3-8910-datasheet.pdf

[2] electro-music.com :: View topic - AY-Voice is Underway

I've read about RC filters that can make temporary 0v after getting 5v again on power up, and tried with different values but can't make it work.

The usual method is a capacitor to ground on the pin. What have you tried that does not work? I've not checked the data sheet, what does it recommend? In the absence of any recommended value I'd try between 0μ1 and 1μF.

You might need a pull up resistor, again, in the absence of a recommended value try 10k to 100k.

You connect the resistor between +5V / Vcc and the reset pin and the capacitor between the reset pin and ground / 0V.

Thanks for answering!

PerryBebbington:
The usual method is a capacitor to ground on the pin. What have you tried that does not work? I’ve not checked the data sheet, what does it recommend? In the absence of any recommended value I’d try between 0μ1 and 1μF.

0.1uF-1uF disc capacitor to ground doesn’t work
The datasheet, given the schematics it provides, recommends a puls from another microcontroller

Also tried 100uF cap and it takes a long time to go from 0v to 5v but after turning the power off and on again, it directly stays on 5v

PerryBebbington:
You might need a pull up resistor, again, in the absence of a recommended value try 10k to 100k.

it has an internal pullup resistor, according to datasheet, it doesn’t states value.

PerryBebbington:
You connect the resistor between +5V / Vcc and the reset pin and the capacitor between the reset pin and ground / 0V.

ok I see, but it doesn’t work either :frowning:

Are you saying that a 100μFcapacitor did work but didn't discharge fast enough when you cycled the power?

100μF seems too high but if it does the job put a diode between the reset pin and Vcc with the cathode to Vcc. That way when you turn the power off the capacitor will discharge into Vcc. If that works try lower value capacitors until it doesn't work.

You need a capacitor to ground powered via a resistor up to supply , with your pin connected between the capacitor and resistor.
The capacitor needs a path to discharge either via the supply or a bigger resistor to ground when the supply is off . ( usually there are other things connected to your supply which will discharge the capacitor - if not put an led indicator on )

Thank you all!!!

I could make it work with your instructions.

It's not perfect, I tried different values and the best is 220uF, but if I turn the power off and on again in less than a second it seems that the cap doesn't discharge fast enough, and it doesn't reset the AY-3-8910 the second time.
If I take more than a second to turn it off and on, then it does and everything is fine.

Any suggestions?

missing from the pic: connection from IC VCC to circuit VCC

keyword for google search: This is how you automatically reset the AY-3-8910 without the need of another microcontroller sending a reset pulse, also called power on reset, or POR :slight_smile:

Glad you got it working. I would expect that you need to turn off the power for more than a second anyway, I think trying to get it to under 1 second is unrealistic. Why do you want it to be under 1 second?

PerryBebbington:
Glad you got it working. I would expect that you need to turn off the power for more than a second anyway, I think trying to get it to under 1 second is unrealistic. Why do you want it to be under 1 second?

Yeah, I know, no problem. As I intend to build a synth with it and sell it, I was thinking the case the user turned it off and on quickly.

When you turn it off and on quickly, there is still some voltage left in the filtering caps of your power supply. The Vcc is not 0V but some higher slowly decreasing value. To get proper reset you need some voltage monitoring circuit that resets the device when voltage is low. They are usually called BOD (brownout detector) or voltage watchdog.