Computing stuff tied to the physical world

More SMD stuff

In AVR, Hardware on Jun 21, 2009 at 00:01

My adventures in SMD miniaturization-land continue:

SOIC chips

Those are two Atmel chips – an ATtiny85 (SOIC-8) and an ATtiny84 (SOIC-14).

Compared to 0603 parts, these are actually quite large. The distance between the pins is 1.27mm (0.05″), half of regular through-hole parts.

But you do need fine tweezers, and a ZIF socket to flash them or try them out without soldering is also nice:

SOIC chips

The lid snaps down, making a firm connection with each of the 14 pins.

Hm, I see now that the SOIC-8 dimensions are a bit wider than the SOIC-14 package. So the smaller package doesn’t fit in this (pricey) ZIF socket.

So not only is this stuff small – it’s also easy to overlook such differences!

Fortunately there are datasheets.

  1. I made that exact assumption, bought the 3M 14pin socket hoping to fit both the Tiny85 and Tiny84 with one socket. Only wish I had stumbled on your site before I placed the order. Lesson learned, Read the datasheets!!!

    Now I have to find a way to program the 85s in circuit with high voltage serial mode, since I needed to use the reset pin as I/O. (The initial flash can be ISP mode, then burn the reset disable fuse. But any reprogram will have to be in HV mode.)

    BTW, very nice blog, lots of good information here.

  2. I am thinking of using a 3M SOIC test clip (digikey number 923650-08-ND) to do in circuit HV serial programming. It looks like this clip will work with standard and the slightly fatter ATTiny85s. Normal precautions in I/O assignments as with ISP, but also make sure anything connected to the Reset (pin 1) can tolerate 12V or a jumper might be necessary to isolate it while HV programming is underway. If you have the ATAVRDragon or the STK500, both of those should allow you to do HV serial programming using the clip.

    For those wondering why go through all this trouble and not just put a programming header in. Usually, when I resort to the 8 pin ATTinys’, size and weight of the PCB is critical (ie. mini model helicopter), plus I can usually get away with a single sided surface mount layout easier without the header and no holes to drill :P

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