This page documents measurements relating to the capacity of the Vectrex to power the PiTrex and associated hardware.

Power Consumption


Measurement was made at the 5V connection to the logic board in the Vectrex. This does not include current supplied to the MOD input of the LM555 IC on the power board, but this current should be minimal.

  • No Cartridge: 0.47A
  • No Cartridge, BLANK asserted: 0.42A
  • PiTrex + Pi Zero: 0.62A

PiTrex Discrete

Measurement of the current consumed by the PiTrex Discrete board's circuitry (3.3V is stepped down from the 5V supply of the Vectrex by the Raspberry Pi Zero board):


  • 0.00061A (0.61mA)


  • 0.00098A (0.98mA)

Raspberry Pi

Raspberry Pi Zero

This is the measured peak power consumption of the Raspberry Pi Zero alone. The power consumption of the Raspberry Pi Zero W is similar.

  • 0.19A

Peak power consumption is about the normal level when running the PiTrex software.

Raspberry Pi Zero 2 W

The review outlink by Tom's Hardware includes the following figures:

  • 0.28A at idle
  • 0.58A under stress

However their figures for the original Pi Zero are significantly higher (260mA at idle and 370mA when stressed) than measured when running the PiTrex software. The lower figure is closer to measurements made with a USB keyboard connected, so maybe they had a USB device connected?


While the original intention was to use Bluetooth as the primary link with peripherals, which avoids power constraints, use of the USB and HDMI interfaces has also been of interest.


The USB specification requires a host device to limit power supplied to a connected device to 100mA until it requests more (in "blocks" of 100mA). Unfortunately the Raspberry Pi Zero does not implement this current limiting, so there's no built-in way to limit power below the 500mA maximum of the USB specification.

Here are measurements of power consumed by some USB devices. This is intended as an example, actual figures will vary a lot between individual models:

  • USB keyboard: 0.17A
  • USB Memory Stick ("Flash Drive"): 0.08A
  • 4-Port USB Hub (no LEDs): 0.01A


The HDMI specification permits connected devices to draw up to 0.055A from the 5V supply.


5V is supplied over two contacts on the Vectrex cartridge connector (more for GND). Each should be capable of about 1A, which is fine. The track going to it on the Vectrex circuit board is also wide enough.

Power Availability

Using the Vectrex as the power source for all of the above rely on three components:

  • The LM340T-5 +5V voltage regulator
  • The 9V output winding of the transformer
  • The heatsinking available (including consideration of heat produced by other components connected to the same heatsink)

The output voltage of the transformer after rectification (the +9V line also used elsewhere on the power board) measures around 12VDC. With good heatsinking the voltage regulator should be OK up to about 1.4A. Measurements of the heatsink temperature indicate that heatsinking is sufficient, with only a 5 degree Celcius increase in the stabilised heatsink temperature when an external 0.5A load was applied to the 5V line, overall reaching approximately 31 degrees above ambient temperature.

The maximum output current of the transformer's 9V output winding is unknown. However the schematics show the 5V line specified at 1A, so it will be assumed that the transformer is safe at this current level.


The Vectrex should be able to supply up to 1A on the 5V line safely. If the Tom's Hardware figures for the Pi Zero 2 W are correct, then this may be right at the limit of the available power, which prevents the use of USB peripherals without risking damage to the transformer in the Vectrex. However their figures for the original Pi Zero also seem high, so it's possible that their figures include power consumed by an undisclosed peripheral attached to the Pi Zero 2 W during their tests.

For the original Pi Zero, there should be capacity for most USB peripherals to be used, though such USB devices must use less than 0.39A.

The power consumption of the PiTrex Discrete board itself is negligible in comparison with the other devices.