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Post by feijai on Nov 16, 2023 23:37:21 GMT
I've recently posted a number of projects for GRAINS. But I may need to yank many of them because I often have to set two pins, namely IN3 and Audio In, to OUTPUT. These are normally analog ins.
The problem is that shorting an output pin to ground, or to Vcc, or to another output pin, will destroy it because it will pull more than 40ma.
I presume the two dedicated output pins (Audio Out, Digital Out) have protection -- like a simple resistor in series. What I do not know is if other pins do. I know that if you change In1 or In2 (which go through the pots) to OUTPUT, bad things happen. It seems that In3 and Audio In work fine as outputs attached to, say, drums or other triggers. But I am worried that some user may attach them to Ground on Master I/O or to +5V on 4ATT-MIX, or to the Braedboard, and if they're not protected...
Does anyone know if In3 and Audio In are protected and safe to use as outputs?
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Post by pt3r on Nov 17, 2023 8:03:32 GMT
You can pop of the frontpanel of the module an have a peek.
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Post by feijai on Nov 17, 2023 9:37:11 GMT
How exactly? What I mean is: how can you tell?
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Post by pt3r on Nov 17, 2023 9:45:00 GMT
you can check whether the pins in question hava a resistor in series connected to it?
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Post by feijai on Nov 17, 2023 10:20:26 GMT
No I got that. I don't know if i can follow the traces: surely these boards are multiple layers.
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Post by feijai on Nov 17, 2023 11:48:10 GMT
I have examined the GRAINS and can safely say that I have absolutely no idea. The traces in question don't appear to be on the outside layers. So I think Tangible Waves is the only one who can answer this question. :-(
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Post by MikMo on Nov 17, 2023 11:59:56 GMT
I think Robert will gladly answer that question, if / when he reads this forum post.
He usually say that every input / output is protected, and you can not blow up anything.
But take his word for it - not mine :-)
If you know which pins on the Atmega they are connected to, could you not just measure resistance from input to pin ?
Mikael
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Post by feijai on Nov 17, 2023 13:58:22 GMT
I believe the In3 and AudioIn are A3/PC3 and A4/PC4 respectively, which according to Atmel's description sheet (page 12) are the second and third pins from the far right respectively on the top edge of the TQFP package chip. My multimeter says that the resistance from the pins to the sockets (module unplugged) appears to be about 4.5 to 4.7 kohms. That's a good sign right? I think that you supposedly just need a 150 ohm resistor to limit the current on the output pin? |
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