I built Tempograf from a full kit to use as an inexpensive master clock. It has four outputs: two duplicated clock outs, a division out, and a reset out. You have two ways to set the tempo, by knob or by a tap tempo button. There’s also a division knob, plus start and stop buttons.

The Build

It’s a straightforward build with adequate instructions that include photos.

Parts come in two paper packages. It’s nice to see paper instead of plastic bags. The PC boards are good quality and the panel is aluminum.

I embellished the appearance by using a black knob for the divisions and put red Bananuts on all of the jacks to make it clear that they are all pulse outputs.

An oddity of the design is that it’s possible to connect the main board wrong way round to the control board.

Operation

There is no user manual for Tempgraf, so I put it on the ‘scope to see what it’s doing.

Clock and division outputs are 0 to +5V, 5 millisecond pulses. The rate ranges from roughly 8 seconds as the slowest, up to 14 HZ at the fastest. This is fine for my use, since I have other modules that do clock division and multiplication.

However, the Reset output looks bizarre on the scope. It rises rapidly to +10V, then exponentially decays to zero over 350 milliseconds, and then repeats the pattern but to -10V. Reset happens the moment that either the Tap or Stop button is pressed. I don’t expect to use it.

You can start the clock either with the Start button or with Tap. Tempo is set by one touch of Tap, the rate being determined by how long it’s held down. I held it down for about 8 seconds and then released, resulting in an 8-second long period. Alternatively, if you press Start, the clock starts at the tempo set by the Tempo knob. Once going, you can switch between free running and tap tempo. Turning the Tempo knob after setting a Tap overrides the tap tempo, and tapping again overrides the knob tempo.

Division

Division output provides a binary division of the clock output, i.e. /2, /4, etc., up to /128. It’s set by a knob and you have to compare the Div LED to the clock LED at the module top. When using the Start button to start the clock, I found that the Div output had a phase offset from the Clock output. When starting with Tap it lined up, that is, the Div output pulse would always come at the exact time as a clock pulse. When switching back and forth between the Tempo knob and the Tap button to change the rate, I saw that sometimes the Div stayed on the clock and sometimes it had the phase difference. In practice, this probably won’t matter, because I’m likely to depend on using Tap to start the clock.