Build a MESA/Boogie BigFoot emulator

Bigfoot is a foot controller used for Dual & Triple Rectifier Head. It uses a non-standard and undocumented interface exposed on 8 pin DIN 270° connector so we need to reverse enginner it.

By disassembling it we can found the name of the pins printed on top of the PCB. After that, with a multimeter, we can observe the signal on that pins.

  • PIN 1 is the GND
  • PIN 2 is the Vcc 5V
  • PIN 8 is disconnected
  • PIN 6, called CH0 is unknown
  • PIN 3 is called V-CH is the only one pin that controls the three channels of the Amps. V-CH at 0,7V meaning CH1 (Channel 1) selected, 1,25V meaning CH2, 1,90V meaning CH3
  • PIN 4 SWB- and PIN 7 SWB+ are connected together and it controls the FX bypass switch. 0V means FX bypass OFF, 5V means FX bypass ON
  • PIN 5 is called SWA and rules the SOLO switch. This pin is 0V when the SOLO gain is ON, and 5V when the SOLO is OFF

Now we can build a simple interface to emulate the pedal board:

Where you see “Arduino” you can use any board that provides some digital outputs. These are the truth tables:

SOLO GAIN
INPUT D4 OUTPUT LED MEANS
0 0 ON SOLO gain is ON
1 1 OFF SOLO gain is OFF
FX Bypass
INPUT D5 OUTPUT LED MEANS
0 0 OFF FX bypass is OFF, so FX chain is active
1 1 ON FX bypass is ON, so FX chain is disabled
CHANNEL SELECT
INPUT D2 INPUT D3 OUTPUT MEANS
1 1 1.90V Channel 3 is selected
1 0 1.25V Channel 2 is selected
0 1 0.70V Channel 1 is selected
0 0

If you want to build a fully working BigFoot MIDI emulator, I’ve developed an open source device based on Arduino: HappySwitch – Open Source MIDI Amp Controller

Carenar 50mm f/2.8 aperture control hack: Auto to Manual conversion

The Carenar 50mm f/2.8 with M42 screw mount was a cheap Japanese prime lens made by Cosina Co., Ltd. with a two blades iris.

Unlike other M42 lenses with automatic aperture control pin, this Carenar can’t be adapted by a ring that keeps the control pin pressed because the pin can be full pressed only if the aperture ring was set to f/16.

On the other hands, if the aperture ring was set to f/2.8, the pin cannot be pressed at all.

Some M42 lenses have an AUTO/MANUAL switch that leaves the pins free to move, but the Carenar 50mm f/2.8 doesn’t have that feature.

The mod consists of replacing the spring between the pin and the lever and unhooking another little spring.


This is the original mechanism. We need to unhook the spring “1” and replace the spring “2” with a larger one.


In the original mechanism the small spring hits the washer of the pin. The new spring needs to be larger than this washer so it can be fitted between the bottom of the barrel and the little lever.


We can get the new springs in a retractable pen.


We need to cut it.


And fitting between the bottom of the barrel and the lever using a little washer on the top of the spring.
If the mod works, the lever that moves the aperture blade is kept against the barrel walls by the new spring and not in the center of the barrel.