Frequency Central CHRONOGRAF Manual
Frequency central
Build documentation for:
chronograf
Featuring code by Jetroid
Main PCB Pots ‘n’ sockets PCB
Chronograf is a super flexible one-shot and cyclic event generator. It can be used as an
envelope generator, LFO, or master clock.
Chronograf features Start/Reset and Stop momentary switches, each with associated
control inputs, as well as a tap tempo momentary switch. A toggle switch selects between
one-shot and cyclic modes.
Four knobs are available to set Tempo, Waveform, Multiplier and Function. There is
another toggle switch to select whether changes to Multiplier happen immediately or at the
start of the next clock cycle.
Chronograf has 5 outputs:
•LFO out
•180 out (same as LFO out but 180° out of phase)
•Clock out
•Start cycle out (Clock divided by Multiplier)
•Reset out (momentarily goes high whenever Start/Reset is pressed)
Waveform selection is chosen by a combination of Waveform and Function knobs. In this
way (arguably) 64 waveforms can be selected.
Bill of Materials
1K x 11
10K x 5
12K x 2
20K x 1
27K x 1
47K x 3
100K x 5
All resistors ¼ watt
metal film.
2n2 x 2
10nF x 3
100nF x 4
10uF x 1
47uF x 2
CHRONOGRAF PIC
TL084 x 4
TL072 x 1
BC547 x 2
1N4148 x 5
78L05 x 1
3mm red LED x 4
14 pin IC socket x 2
8 pin IC socket x 1
B100K x 4
10K trimmer x 1
3.5mm socket x 7
SPDT switch x 2
Tactile switch x 2
Momentary switch x
1
Male header x 1
(cut to size)
Female header x 1
(cut to size)
Power header x 1
Main PCB assembly
1. Solder the diode and all resistors
2. Solder all three IC sockets
3. Solder the non elecrolytic capacitors
4. Solder the 78L05 –watch the polarity!
5. Solder the box power header. Make sure the notch lines up with the screenprint
legend. If in doubt, have a look at a power cable, and make sure when inserted into
the header the red stripe lines up with the -12V screenprint.
6. Solder all electrolytic capacitors and the trimmer
7. Cut male headers to size and solder them into place. Make sure that they stick out of
the bottom of the PCB.
Main PCB minor modification
Chronograf puts out a reset pulse when Start/Reset is pressed.
We realised that for some applications it would be useful
for Chronograf to also put out a reset pulse when Stop is
pressed. It’s an easy mod, just add a 1N4148 diode as shown
to the rear of the PCB. We recommend that you perform this
mod when building your Chronograf. Later versions of the PCB
will include the mod, and will state ‘No mod needed’on the
back of the PCB.
Pots ‘n’ sockets PCB
1. Place the PCB on a flat surface. Place the
2 tactile switches into their solder pad.
Do not push them all the way through,
they should sit proud of the PCB (see
photo), their legs should not protrude
through the other side. Solder them into
place from the top of the PCB.
2. Solder the 4 potentiometers, the 2 toggle switches and the Tap LFO momentary
switch. Use the panel to make everything line up nicely.
3. Place all sockets on the PCB, making sure the ground tabs line up with the PCB’s
ground pads –be careful because there are two different orientations - then place
the panel over them. This will assure that the sockets are correctly positioned. Flip
the whole lot over and solder the sockets into place. Use cut off resistor legs to
connect the sockets’ ground tabs line up with the PCB’s ground pads.
4. Cut female headers to size and solder them into place. Make sure that they stick out
of the bottom of the PCB.
5. Put all 4 LEDs through their pads. Present the panel to the PCB, flip the whole lot
over, make sure the LEDs stick though the holes in the panel, solder in place.
Calibration
The Offset trimmer, as you might guess, adjusts the offset of the LFO waveforms. Take a
DMM, connect the black probe to ground and the red probe to the test pad next to the
trimmer. Adjust the trimmer until you read -1.6V on your DMM. The waveform should now
be centred with respect to 0V.
All done! Go play!
