The Joat

The Jack-of-all-trades

On occasions, I've had the need to:

• measure the frequency of an oscillator.
• measure the value of a capacitor.
• measure the value of an inductor.
• program an AVR microcontroller (for example an AtTiny85).
• reset the "fuse bytes" of an AVR microcontroller. Well, OK, I haven't needed to do that yet, but the time will come...

Every time I've wanted to do this, I've knocked together a temporary gizmo using an arduino nano and a breadboard full of hookup wires and odd components. And then afterwards I've dismantled it.

So I decided to build a more permanent gizmo with a display and a crude user interface that can do all of the above and maybe more.

This page is intended to provide the binary files (photos, circuit diagrams etc.) of the project. When I get a round tuit.

Display

Just about any old 2x16 LCD with a standard parallel interface would serve. I used an old LCD-compatible VFD that I had lying around. If you have an LCD with a serial interface you might have to bit-bang it because the AVR programmer uses the SPI.

Pushbuttons

Only two buttons are needed. They are multiplexed onto a single analogue input of the arduino with a resistor ladder. You could easily extend this to three or four buttons if needed. Or maybe more.

Schematic and matrix-board layout

Click image for a larger version.

Photos

Coming "soon".

Source code

The source code and other technical information for the project is on Codeberg, GitLab and GitHub.

The round tuit dept.

I still need to add the switchable 12v supply to power the AVR for resetting the fuses and add another mode to the menu to do the deed. I'll build that feature when I get a round tuit. Or when I desperately need it, whichever happens first.

Use cases

Here are some of the jumpering schemes for programming AVR microcontrollers.

Programming an AtTiny85/45/25/13

Tested on AtTiny13 and AtTiny85.

Make the following connections:

Signal	J.no.	ZIF pin	AtTiny pin
Vcc	J1.6	40	8
Gnd	J4.x	4	4
RST	J1.5	1	1
SCK	J1.8	39	7
MISO	J1.9	38	6
MOSI	J1.10	37	5

Insert the AtTiny so that pin 1 of the MCU is pin 1 of the ZIF socket.

avrdude options:

avrdude  -b 19200 -c avrisp -p t85 ...

... or -p t13, -p t45, -p t25 as appropriate.

Programming an AtTiny84/44/24

Tested on AtTiny44.

Make the following connections:

Signal	J.no.	ZIF pin	AtTiny pin
Vcc	J1.6	1	1
Gnd	J4.x	40	14
RST	J1.5	4	4
SCK	J1.8	35	9
MISO	J1.9	34	8
MOSI	J1.10	7	7

Insert the AtTiny so that pin 1 of the MCU is pin 1 of the ZIF socket.

avrdude options:

avrdude  -b 19200 -c avrisp -p t44 ...

... or -p t84, -p t24 as appropriate.