ATTiny Nano Programmer

This is a project to make an ATTiny programming "shield" for the Arduino Nano. Some of the aims of this project are as follows:

1. Features an ATTiny DIP socket.
2. Roughly the same size as the Nano.
3. A 10uF capacitor on the Nano's RST pin to ground.
4. An LED for the Nano.
5. An LED for the ATTiny. 
6. Maybe a reset switch for the ATTiny.
7. Maybe IO headers for the ATTiny.
8. Maybe purple.
9. Use an auto-router.
10. Learn net classes and stuff.

Why a Nano? To be honest, I'm not really sure why I've grown so attached to the Nano. Perhaps it's because it adapts more easily to a breadboard than the Uno. Maybe it's because that was the first microcontroller board I used. Maybe it's the minimalist form factor.

Next up, layout!

UNI-T UT61E Backlight, Part 3

All that's left is the sense pad. Which means I need to figure out an appropriate size. I'm using a brass strip that's 1/2" wide by 1/64" thick because it's easy to solder and bend. I know the meter's case isn't the thinnest so I'll use some polycarbonate (.24" thick) for testing different sizes. The main thing is I want a finger touch to turn the light on, not a finger passing nearby or a finger hunt.



My test board is soldered to a longish piece of wire and 2-1/4" long brass strip.



A 1" long strip works reliably, however a touch area that's too small could mean hunting to switch the light on.



I settled on a 1-1/4" long strip and it just so happens to fit nicely into the back cover.

 

Soldered in and covered in Kapton. I also wedged a little piece of foam by the buzzer to hold the sense wire in place. Time to put it back together.



Actually closing the meter wasn't tricky or difficult. The backlight is a little dimmer than the picture above but overall I'm very happy with the mod.

Since I have a second board, I put 9V on it and measured the current draw. The UNI-T measures about 10µA but measures a max peak of 30µA and min of 4µA. So something is going on but I don't have a scope to investigate further and I'm pretty content letting it be a mystery ... for now.

The last picture above shows 1.76V on the test board which still registers touches and lights the led! You do have to cycle the power between large voltage changes to allow the TTP-223 to re-calibrate. I'm really pleased with the TTP-223. It just works. It's not finicky or complicated to integrate which is perfect for my skill level.

To be continued ... maybe with battery tests ... 

UNI-T UT61E Backlight, Part 2

Testing LED's, left to right:

1. 3mm LED's from Amazon (cheapest and brightest)
2. Lite-On LTST-S220KGKT
3. LG Y876-P1Q2-24-Z

The cheap LED's are running at 3.5mA while the other two are at 7.5mA. I'm curious why the huge difference in light output.

Since I wasn't planning on 3mm LED's, the backlight board doesn't lay flat. I had to do a little choppy-choppy on the board and the LED's.

Onto the touch board, it works ... first time! My sense pad is a blue tape covered scalpel blade.

 Installing the touch board. Kapton tape on back as a little buffer. Power leads connected.

And a lot more Kapton on top after backlight and sense leads attached.

To be continued ...

CadSoft EAGLE + Single Layer SMD Design = OSH Park Errors

Problem: Recently designed a single layer board with only SMD components, but copper pours on both sides. Upon uploading to OSH Park, I got several errors like "no bottom mask", "no bottom silk" and "drill file missing". To move forward, you have to approve the design by selecting a check box.

I didn't want my component-less bottom copper to lay unmasked against other components after installation.

Answer: To keep OSH Park from throwing errors and also include bottom solder mask and a drill file, place a via outside the board's perimeter. This in essence  creates a 2-layer board from a 1-layer design.