Amateur Radio – remembering Ohm’s Law with the VIR triangle (and the PIV triangle)

For the Amateur Radio license exams (for most countries) you need to remember Ohm’s Law, which is easily remembered by the Ohm’s Law triangle:



V = voltage (volts)

I = current (amps)

R = resistance (ohms)

To calculate any value knowing the other 2, cover the value you need with your finger and then use the remaining calculation, e.g.

V = I x R

I = V / R

Similarly for Power, use the PIV triangle:



P = power (watts)

I = current (amps)

V = voltage (volts)

VT132 assembly: USB add on board notes

There’s no explicit instructions on the VT132 website for how to attach the optional USB addon board instead of the default PS/2 connector but there is an extremely details step by step video here.

Summarizing the additional steps:

  • trim the 4 back legs of the USB connector so that it sits flush to the red addon board and make sure the pins don’t protrude from the board, then solder the back pins to the add on board and make sure the soldering is flush so it will sit flush to the main board
  • solder the 2 larger outer pins from the back first, then the inside 2 pins
  • the addon board attaches to the main board component side up
  • push the black spacer of the 6 pin header all the way down so the spacer is flush to the end of the pins
  • attach the row of header pins though the top of addon baord to the back; there shouldn’t be any length of the header pins extending on the top
  • solder the header pins on the back of the addon board
  • put a small strip of electrical tape across the bottom side of the addon board before inserting to main board before soldering, to avoid any contact with the original PS/2 connector pads on the circuit board
  • insert the addon board, turn over and solder the pins
  • solder the two front structural legs on the usb connector

VT132 kit assembly – step by step

I’ve just finished assembling my VT132 standalone kit from The High Nibble. It was an enjoyable build and pushed my soldering skills with soldering the tiny pins on the ESP32 chip. Initially I had issues getting solder to flow onto the tiny pins and pads, but I changed to a thinner tip which worked well.

Here’s a look at the board as it comes in the kit. I chose the option USB keyboard option instead of the default PS/2 keyboard connector:

Starting with the ESP32 first, here’s a look at my soldering on those tiny pins. I used the liquid flux, and the ‘drag’ method to pull the solder from the pads up to the exposed connector on the chip board:

Row of resistors for the VGA connector completed, and a few of the caps:

Almost done, just need to attach the DB9 and DB25 connectors:

First power on and looking at the settings. To access the ‘Set-up’ from a regular keyboard, press Alt PrtScrn. To view the onscreen menu help press F1:

More details on using the VT132 coming up in following posts.

Ten retro computer electronics kits you can build yourself

I’ve just started work on assembling the VT132, a DEC VT100 compatible terminal. I got the standalone board, but there is also a version as an add-on board for the RC2104 computer. Not knowing anything about this, it turns out it’s a kit to build an 8 bit Z80 based computer that has expandable card slots for other add-ons. I might look at building one of these next, but out of interest I wondered what other similar kits are out there for building reproductions of retro computers. I noticed it’s not uncommon for some of these to only be produced in limited quantities and it’s unclear whether they will be available again, but here’s a list of things I’ve found:

Wifi232 – an RS232 modem that connects to your wifi instead of a real phone line. This was only produced in limited quantities but is well known in retro computer communities as an easy way to get any old computer with an RS232 interface online. More info here. If you search around you can find a few alternatives and similar kits inspired by the original Wifi232.

IBM PC 5150 motherboard kit – no longer for sale, but an impressive kit to build your own reproduction of the motherboard for the original IBM PC.

Apple 1 reproduction kit. No long available from Briel Computers, but check their link for other suppliers who may still be making the kit.

RetroBrew computers – several kits for Altair/S-100 bus type computers

Altair 8800 kit – no longer available?

PDP-8 and PDP-11 replicas front panel kits and emulation using a Raspberry Pi by Obsolescence Guaranteed

Harlequin 128 – reproduction of the Sinclair ZX Spectrum 128

Cobalt 3 – a Atmega328 based 8 bit pocket computer

If you know of any others leave a comment!