Monday, October 19, 2020

feegle

Tiny 40%

A 4x12 matrix the same size as the Gherkin Express TH and using the same 6x6mm tactile switches.

The switches are rotated so that the through hole pins are staggered allowing the switches to be placed closer together.

The power and activity LEDs from the Gherkin Express TH are removed. Instead the blue LEDs for V-USB voltage regulation are used as a power indicator, and a flickering activity indicator. 

The miniature 16MHz crystal is also used as on the second version of the Gherkin Express TH.

There is only one decoupling capacitor instead of the usual 2.

The 1mm thick top PCB has legends in the copper layer.

The two blue LEDs on the corner, D- on the left and D+ to the right. D+ is always on while connected to USB. D- flickers when data is being transmitted.

The two red switches are the RESET and USBASP switches for entering the V-USB bootloader.

Everything fits with 4mm M2 spacers. Construction is the same as with the Gherkin Express TH.

Same credit card size as the Gherkin Express TH. It shares the same bottom PCB. Screw holes are in the same positions.


Thursday, October 15, 2020

Wee Gherkin

No'-as-big-as-medium-sized-Gherkin-but-bigger-than-wee-Gherkin Gherkin

Another Gherkin in a different form factor. This shares the same circuit and firmware as the Gherkin32. It is also powered by an ATmega32a. The main difference is the form factor and the use of 3.5x6mm tactile switches. It also uses blue LEDs instead of zener diodes in the V-USB circuit.

3.5x6mm tactile switches only come in 2 heights, 4.5 and 5mm. This is too short to make a usable top plate. The rectangular plunger also wobbles on the short axis more than the long axis. These black switch are from Digikey. There were very few options, and only black available.

These were cheap switches bought from a third party seller on Amazon. They are horrible. About a quarter of them do not click. They do work, just no click when pressed. Most sellers refer to these at 3x6mm but they are really 3.5x6mm.


Wednesday, October 7, 2020

Gherkin Express 3

Third SMT assembly order from JLCPCB

This version uses the same circuit as the Gherkin Express 2, but with blue LEDs instead of the zener diodes. It also uses the PCB as a USB A connector.

All parts used were available in the JLCPCB inventory. Only the fuse and the tactile switches had the setup surcharge.

The board will plug directly into a USB A port, or an extension cable. The 1.6mm PCB is on the thin side. Ideally it should be 2.2mm thick to fit properly. JLCPCB has 2mm PCB as an option, but not with assembly. I'm considering haveing a 0.6mm thick blank PCB with the same outline made and laminate the two PCBs together.

Monday, October 5, 2020

Copper legends

Sanded the soldermask off to expose the copper

I used 220 wet/dry sandpaper to carefully sand the soldermask off the copper. I also used a Scotchbrite pad to dull the surface of the remaining soldermask.

The copper is starting to oxidize and turn darker. I could spray some clear acrylic to seal it.

I also sanded the bottom of the PCB. This looks neat, but is probably a bad idea. The soldermask not only protects where solder can be applied, it is an electrical insulator. They make conformal coatings specifically designed to protect PCBs, but they have highly flammable solvents and I can't find any locally. Shipping for a small bottle is very expensive. If you are using leaded solder this is a very bad idea, creating lead dust.

Friday, October 2, 2020

Gherkin Express TH 2

Second version of the through hole Gherkin Express

Main changes from the original Gherkin Express TH are the miniature 16MHz crystal and the mini USB connector is moved inwards to be flush with the edge of the PCB. The zener diode footprint is overlapped with one for a blue LED.

The switch positions and LED cut outs are the same as the first version.

I made a new top piece with the legend in the top copper layer instead of the silkscreen layer. The resolution of the copper layer is much higher than the silkscreen. Green, blue, red and yellow soldermask is translucent and the legends can be read through them.

M2 spacers with M3 unthreaded spacers. With the shorter crystal and a smaller 3mm diameter power capacitor laid down on it's side, everything fits with 4mm spacers.

The two zener diodes were replaced with rectangular 2x3x4 (4mm tall) blue LEDs. The power capacitor on this one is a 4mm diameter solid polymer capacitor.

Blue PCB top piece. This one is 1mm thick, the green one was 0.8mm thick. It is a bit stiffer but does not make that much of a difference.

4mm spacers and a 1mm thick nylon washer between the bottom PCB. The top screws are 3mm and the bottom 6mm.