Guþ Cleadur - Clock + Divider
For Guþ Cleadur's main clock, I started out from the schematic for Synthrotek's 555 Timer chicklet, substituting the 7555 CMOS version that offers improved performance over the standard 555 timer. I wasn't really happy with the output though: The duty cycle of the clock ranged from approx. 60% to over 99%, depending on the frequency.
After some pondering, I decided to use a 4013 d-type flip-flop ic to divide frequency by two thus achieving a fixed duty cycle of 50%.
Sadly, the 4013 had problems reading the 7555 output, it was just too skewed... So, after reading this very informative Electronics Tutorial, I added a couple of diodes between the 7555's trigger and discharge legs and voilà, main clock working steadily at frequencies of about 0.5-500Hz.
The main clock is sent to a frequency divider through the switching contact of an audio jack. That way, I can sync the Guþ Cleadur to an external clock that'll overwrite the internal one.
The divider circuit is based on Fonitronik's Simple Divider design that makes use of a 4024 7-stage cascading binary counter for divisions. I'll stick with the original design and use only the 1⁄2, 1⁄4, 1⁄8, 1⁄16 and 1⁄32 divisiond. The 4024 IC could deliver two more divisions (1⁄64 and 1⁄128) but 6 different timings will be enough for now.
The output of the 4024 is sent through a 4069 inverter ic, so all division outputs will start high on one.
The inverted divisions are conditioned through a 2n3904 NPN transistor and split threeways: One copy of the signal is sent to each channel's "division-chooser" SP6T rotary switch. Furthermore, each division is sent to an output jack for syncing external gear like sequencers or whatnot.
Next on my agenda will be the Logic and ADSR circuits and of course the interface.