ISP programming header on v1.2?
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ISP programming header on v1.2?

by osbock on Fri Oct 21, 2011 1:44 pm

I recall that I couldn't use the ISP programming header on v1.1 if the LED's were already soldered on, essentially because the serial programming voltages would get sucked into the LEDs. Is this correct? Is it still the same with the new transistor configuration in 1.2?
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Re: ISP programming header on v1.2?

by adafruit on Mon Oct 24, 2011 10:42 am

you should try it, we're not sure - we think its a bit better now but you might have to clip the resistor off and then re-place it
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Re: ISP programming header on v1.2?

by osbock on Wed Nov 02, 2011 9:36 pm

I finally got around to soldering the header on and trying the programming. (I left it off, because I found it wasn't useful in v1.1)
Programming definitely doesn't work without lifting the resistor. Someone asked on my instructable, and I said I didn't think it would work with the drive hooked up, and now it is confirmed (at least with USBTinyISP). Lifting the resistor (R1), programming works fine.

No biggy for me, except I'll probably bend the pins too much one of these days, but the attiny85s are cheap.

There might be a single position dipswitch that would fit in the place of R2, that some might want to bodge in there...(cutting traces, etc.)
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Re: ISP programming header on v1.2?

by PorkRhombus on Tue Oct 30, 2012 4:33 am

Having just accidentally tried it, I would strongly recommend you don't try reprogramming in-circuit via the 6-pin header. Not only did it not work, but it left the chip corrupted, requiring me to pop it out and reflash it.

However my main concern in this situation is for the LEDs and transistors, since they would see high continuous currents if the programmer holds the MOSI line low, which it might well do. I've noticed subsequently that the LEDs in each pair are quite different in brightness. Perhaps that was the case before ( without base or collector resistors, slight differences between individual transistors and LEDs could result in the current being shared quite unequally) or perhaps it is a result of this failed in-system programming attempt. I don't know, but If there is ever a v1.3 I would like to see a few more resistors. Having said all that, it still works ...

If it's really important to you to be able to reprogram in-system, I would suggest installing some single-pin sockets into the R1 and R5 (or LED) holes. Then you can just pop out those components to isolate the chip from the rest of the circuit. Just get one of the nice type SIP or DIP sockets with the round holes and with an X-acto knife carefully liberate the individual metal sockets. These are well handy for prototyping where you want to be able to easily change out individual resistors, caps etc.
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