Boss DR-110 Clap Pulse Generator (trigger adapter)

Here's a circuit I came up with a while back. I had a DR-110 with a dead digital board. The digital board is responsible for generating all the triggers in the system, and it generates some very specific triggers for the clap circuit. 

CPI is three 1ms long pulses, every 10ms (100hz).
CPII is a separate pulse also 1ms long, that falls 10ms later.

I re-implemented this in the following circuit.
Traces from top to bottom are CPI, CPII, and Trigger in.

The traces are from a simulation of the circuit, that you can play with in real time here.

Breaking down the circuit, we start at C8 and R11. These form a hipass filter for the incoming trigger. This ensures that long triggers will be handled the same way as short triggers.

IC6A & B are schmitt NAND gates and they form an SR latch. It is set by an incoming trigger, and is reset by the CPII pulse. The output is used to enable the generation of the CPI signal.

IC6C is the core of an oscillator that can be enable/disabled from pin 8. It works by charging and discharging C9.
R14 sets the charging rate of C9, and determines the low time between pulses.

R15 and D4 set the discharge rate, and determine the length of the pulses.

R12 & R13 help bias C9 near the threshold voltage of IC6C. This ensures that the first pulse will be close in length to the following pulses. If C8 had to charge all the way up from ground, the first pulse would be much longer.

IC7 is a counter, and is keeping track of how many pulses have been seen on CPI.
Once the end of the third pulse is counted, output QC goes high. This resets the SR latch, disabling the oscillator, and very quickly stopping the fourth trigger.

Output QC is also used as our CPII signal. To limit it to 1ms in length, we use it to charge C7 through R9. After about 1ms, C7 has charged enough to trigger the CLR pin of the counter. This causes output QC to go low again and discharge C7.

So, with some simple tweaking, this circuit can generate different lengths, rates, and numbers of pulses.

DR-55 Battery Backup

I made a simple adapter to run my DR-55 from a wallwart instead of a battery. The DR-55 uses the battery to preserve the pattern memory, and my adapter forced me to remove the battery. So, I added a coin cell that is able to retain the patterns, and leaves room for my adapter.

This modification might still be useful without the wallwart adapter. It lets you remove, or run down your AAs without losing your patterns.

The modification requires:

• CR2032 Battery
• Insulated Battery Holder
• IN5817 Schottky Diode 

Optional parts:

• JST Wire Connector
• Heat Shrink Tubing

I chose to replace the battery wires with JST terminated wires. This makes it easy to remove or replace the battery holder. I think it's nice to be able to easily "undo" a modification.

I then soldered a schottky diode in series with the battery. This prevents another power source attempting to "charge", and destroy the CR2032 coin cell. A schottky diode is used for the low voltage drop it offers. This lets the RAM see a higher voltage from the battery, and function longer as the voltage decreases.
The white line of the diode points away from the battery, and the other end is soldered to the red wire. A little heat shrink tubing keeps the diode lead, and wire, from shorting anything.

I attached the battery as shown across capacitor 39, as it bridges the RAM's supply pins.

I closed the machine up and slid the battery holder between the case and PCB. It can also be mounted in the battery compartment with some adhesive foam.

That's it! Make sure the holder is switched to "on" and that you put one battery in it. The holder is made for two batteries, but works fine with just one. In fact, two cells offer a bit too much voltage for the RAM, and may shorten its life.