Program SOIC 8 in-circuit without header

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One of my current projects uses an ATTiny25 on a very small PCB. I'd like to be able to HV program them using an STK500 and something like this: http://www.all-spec.com/products/5250.html

Is this a good solution, or is there something else I should look into?

Thanks!

I have too many hobbies.
s-conductor.com

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Can your circuit handle the brief 12V on the reset line?

The clip should work, depending on how much space there is around the chip. I don't know how much clearance the clip needs.

Is this for development/debugging or series production programming? For the first, I'd just solder wires to the pins for a more reliable connection that isn't easily disturbed, mechanically speaking.

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There is a small line driver on /RESET.

I'm glad you asked about that because now I'm questioning if I've read the datasheet correctly. It says -0.5V <-> 6.5V at the inputs, but has a note which says:

Quote:
The input negative-voltage and output voltage ratings may be exceeded if the input and output current ratings are observed.

I've looked in the STK500 user guide but can't find any electrical characteristics for the HVSP/HVPP.

Programming in-circuit should only be necessary during development, but when I make a change it needs to be applied to 32+ devices. So, I was hoping for something I could use to quickly iterate (if necessary).

http://focus.ti.com/lit/ds/symlink/sn74lvc2g34.pdf

I have too many hobbies.
s-conductor.com

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The reset line can stand the 12V programming pulse, because it has no protection diode to VCC as all other pins do. In the AVR guidelines is it recommended to add this diode externally to improve transient immunity. If you have followed this advice, which I don't know, you might temporarily lift VCC above maximum ratings if there is not enough low impedance in the system to handle it. Or maybe you have used the reset pin as I/O.

Are you sure you need HVSP and not regular ISP? HVSP is only needed as a last resort if you mess up the fuses and regular ISP becomes impossible.

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Thanks for the replies.

Yep, I am using RESET(PB5) as IO, which is why I might need HVSP. Unless of course my software is perfected before I make a production size run... :)

I'm not worried about the AVR under HVSP, but I am concerned about the buffer on the same line (it's used to drive an LED), since one of its inputs will see 12V for a brief period.

I have too many hobbies.
s-conductor.com

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I think I'll add a jumper to the PCB in case I need to program the AVR and protect the inputs of the buffer.

Does anyone have a recommendation for a jumper style to use? I normally use a .1" spaced through-hole male header, but board space is limited and I'd like to find something smaller (solder bridge?) if possible.

Thanks

I have too many hobbies.
s-conductor.com

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What kind of driver chip do you use ? It might be
enough to place a resistor between the driver and
the AVR. This resistor would limit the current
to the driver. If the driver has a CMOS input and
you don't need high speed a 10k resistor will do
the job.

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If the reset pin drives a LED when used as GPIO, maybe it would be possible to skip the buffer and just have say 1k resistor there, with 5V GPIO you get 3-4 mA current, with 12V reset pulse, you just get 10-11mA current.

Or a transistor, that does not care if the base current is 0.5mA or 1.2mA...

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Quote:

I'd like to find something smaller (solder bridge?) if possible.
Also known as 0 Ω resistor. Available in all typical SMD sizes from many, if not all, SMD resistor manufacturers.

Stealing Proteus doesn't make you an engineer.

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Or maybe use ISP. I put the 6 pin header pads, but not the header itself and put "pogo pins" on my ISP programmer.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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ossi wrote:
What kind of driver chip do you use ? It might be enough to place a resistor between the driver and the AVR. This resistor would limit the current to the driver.
The RESET/PB5 pin is very weak so I want to keep the resistance as low as possible between the AVR and buffer input. Here is the datasheet for the buffer: http://focus.ti.com/lit/ds/symlink/sn74lvc2g34.pdf

Quote:
If the reset pin drives a LED when used as GPIO, maybe it would be possible to skip the buffer and just have say 1k resistor there, with 5V GPIO you get 3-4 mA current, with 12V reset pulse, you just get 10-11mA current.
I definitely need more current (20mA+) than the RESET pin can sink alone.

Quote:
Also known as 0 Ω resistor. Available in all typical SMD sizes from many, if not all, SMD resistor manufacturers.
I think this will work well. Thanks!

Quote:
Or maybe use ISP. I put the 6 pin header pads, but not the header itself and put "pogo pins" on my ISP programmer.
I will be programming them using ISP (the high-voltage version available on the AVR I'm using). I like your idea of using pogo pins instead of mounting a header. I'll probably add this to my next design.

Thanks again for all of the suggestions.

I have too many hobbies.
s-conductor.com

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I use pogo pins for mine, got the pins on ebay for a good price.

I have plated holes for where the pogo pins make contact on the pcb. The holes are too small for the pogo pins to actually go through, there are there so to stop the pogo pins from slipping around.

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It will work, and you chose a good clip. Pomona - accept no substitutes. The 3M clip is NFG, the spring is too strong and it doesn't grasp the package. The Pomona clip is just right for 0.15" packages. It fits the 0.3" wide package less well, but adequately. It doesn't last very long in production, though - after a hundred or two pieces you'll have to replace it. The spring contacts bend, wear and break off, and the tiny teeth at the corners that grip the package burr up and break.

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Just a follow up... The Pomona clip works very well for both the .15" and .3" packages (different revisions of my PCB - damn AVR availability).

I'm crossing my fingers, but the code seems to be solid enough I won't need to worry about HV Serial Programming anyway.

Thanks again for the help/suggestions!

I have too many hobbies.
s-conductor.com