I haven't included the connections required for external expression pedal rate control, opting to keep it self contained, but if you do want to include one, make the connections to the control socket to where the rate pot currently connects to the board, as shown in the scheme on the Moosapotamus site.
Info from Moosapotamus about their pedal:
The SKIPPY tremolo is based on the vintage Vox Repeat Percussion. The original VRP is well known for it’s very hard, percussive tremolo sound, or chop. Certain combinations of speed settings and playing style can almost trick your ears into thinking that you are playing through a delay instead of a tremolo. For these reasons, the sound of this tremolo effect is often described as synth-like.
Originally, the VRP had only one control, Rate, to adjust the speed of the effect. In addition, the version that was built into the Vox Beatle Super Reverb amplifier also had an input jack for a foot pedal that enabled you to control the speed of the effect with your foot.
With additional controls and features, SKIPPY covers a much wider sonic range while still retaining all the character and bravado of the original VRP. Check out the video…
Depth - Adjust effect depth from subtle throb to hard chop.
Rate - Adjust effect speed.
Level - Adjust output volume to compensate for perceived volume loss with certain extreme settings.
Tone - Switch original Vox low-cut filter on or off. When on, output has a lot of treble and very little bass.
Mode - Switch between hi and low speed ranges. Low speed is normal tremolo range. Hi speed is pseudo ring-modulator range.
Plug CV pedal into control jack to vary speed with foot while playing.
Capable of ultra-wide range of speeds, up to pseudo ring-modulator speeds.