ATTiny Nano Programmer, Part 3

Assembly

The boards* are in and ready to be populated with the proper components listed on the BOM whatever i can find in my scrap bin. For the very first assembly, I'm using female headers on the Tiny board so i can easily remove it from the Arduino Nano in case something goes wrong.

So I've exhausted my supply of female headers so the first assembly looks a little lame. But it works. And since it works, one should know that this board has no voltage regulation and no polarity protection diodes of any sort. So be careful!

Programming

The ATTiny isn't supported out of the box by the Arduino IDE, but MIT's hi lo tech has a handy-dandy tutorial for adding the ATTiny support and programming it.

To program the ATTiny, the Nano first needs to be programmed to be an ISP. The RST cap on the Tiny board is disabled by 1) moving the jumper to the position closest the USB connector or 2) removing the jumper altogether. The ArduinoISP sketch can be uploaded and the RST cap moved back to enable programming the ATTiny.

A note on clock settings and fuses: If you want your ATTiny to run at a specific clock speed, select the desired frequency under Tools - Clock and then under Tools - Burn Bootloader which sets the approriate fuses. Once the fuses are set, you can upload your sketch. If you switch the clock speed without "burning the bootloader" and upload a sketch, your timings might be off, e.g. a 1 second delay is now 8 seconds or vice versa.

Features

The red LED is for the ArduinoISP heartbeat and is a breakout of the Nano's D9 pin. The green LED is an onboard LED for the ATTiny and connected to D3 (not D1), see bright green highlight. This LED can be disabled by the nearby jumper. There's a 3.3/5Vvoltage selection jumper (blue highlight) for when this guy is attached to the Nano. Again, there's no voltage regulation/protection apart from the Nano's.

 

Testing

Tested

1. Digital IO/Analog outputs
2. V+/V- connections
3. LED/RST Jumpers
4. RST button

Not Tested

1. Analog inputs
2. 3.3/5V jumpers
3. VIN header

Files

EAGLE files, PDF's here.

BOM

2x   3mm LEDs
2x   220 Ohm Resistors
1x   10uF Capacitor, Radial
1x   Momentary Tactile Switch
1x   ATTINY85-DIP (Digi-Key AE10011-ND)

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*I used OSH Park's new 2 Layer 2oz 0.8mm Service because I'd never used it before. The board is nice and thin, alignment and silk both look great as usual.

ATTiny Nano Programmer, Part 2

So layout went rather quickly on this one because it's pretty simple and I have too much fun doing this. Actually, the board is already on order with OSH Park.

I took some (read a lot of) design cues from Kevin Rye's ATTiny Programmer. Among other things, I liked the LED disable jumper, the IO breakout headers and the idea to create a programming board that one can also use in a project. I elaborated on the IO breakout by adding V+ and GND headers. Maybe it will be useful, maybe not. I also added a jumper to selected 3.3V or 5V and another to enable/disable the 10uF cap on the Nano's RST pin. There's also a dedicated RST switch for the ATTiny.

The overall profile mimics the Nano's with an extension opposite the USB connector on the Nano.

So here's the final design ...



And the schematic ...




Now I play the waiting game ... and discover where I screwed up. Which was ignoring a poorly placed via and at least one silkscreen mislabel. In the meantime, I've learned how to cover the vias with soldermask using Masks tab in the DRC. The final-er design is below.