Hihat Dilemma - Megadrum 32 input build

[midnightlamp]

Hi all,

Just finished up a 32 input build with Jobeky cymbals and mesh heads on a custom built kit. Almost everything works but I'm stuck on the hihat. The issue I'm running into is with the hihat pedal.

I'm using the optical hihat circuit described here. This is how I've set it up: R1 is 150ohm, R2 is 5k6 ohm, C1 is 0.1uF (all as per the schematic) - and it's a tantalum capacitor (non polar), LED1 is a superbright white LED (also have a yellow one but this produced higher output), and Photo1 is VTT9812FH which has a sensitivity of 585nm. The diode is a 1N4148, but also tried a 914 and another 4148 I had to verify. I had also previously used the Radio Shack IR pair as suggested in the thread above. I also have a few other phototransistors to try.

The circuit works on the breadboard, works when I assemble my controller (did a 3D printed controller I'll be posting up about), in that when I supply 5V to the sleeve, ground the ring and probe the voltage from Ring to Tip it varies from ~3.78V (open) to almost 0V (closed). When I throw that on the module though - this doesn't work correctly at all. What I see is the following: If the impedance switch is set in the "up" position I get a signal reading of ~300 on the unit and in MDM. If I put it to the "down" position, I get a reading of 90 - neither move. When I measure off the module using a raw TRS cable plugged in I get 5V (sleeve to ring). When I plug in the controller I made and measure this drops to 2.94V or so. By blocking the diode, the output varies from 2.685V (fully open) to 2.700V (blocked).

My other settings: new alg is off, reverse levels is off, auto level is off, pedal type is foot controller. What I'm watching is the number on the MD display.

Any help would be much appreciated!

[midnightlamp]

An update on this - It looks like one part of the problem is the LED itself. I needed to go with a much brighter smaller LED (which I did) and decrease the separation distance. With a smaller even brighter LED (1.8mm instead of T1-3/4), and a slightly lower resistor (120ohm) the brightness goes up a bunch.

I played around with a few settings and components.
- If I use a value of 10k for R2, and power the LED separately through my power supply I get a range of 847 open, down to 472 blocked. This is with the impedance switch up and alt input disabled.
- If I do the same as above but power the LED from the megadrum I get a range of 536 open, down to 349 blocked. This is with the impedance switch up and alt input disabled.

[dmitri]

- If I use a value of 10k for R2, and power the LED separately through my power supply I get a range of 847 open, down to 472 blocked. This is with the impedance switch up and alt input disabled.
- If I do the same as above but power the LED from the megadrum I get a range of 536 open, down to 349 blocked. This is with the impedance switch up and alt input disabled.

Either of these levels ranges are perfectly suitable for the pedal to work correctly.
Did you disable AutoLevels in the Pedal settings?
Did you set High and Low levels in the Pedal settings accordinggly?
What is the actual problem with the pedal with these settings?

[midnightlamp]

Hi Dimtri - yup, redesigned my housing for this to place the sensors as close together and possible and bumped up the brightness and that seems to have solved it. I'll post in the optical hi-hat thread with some more details for anyone in N/A that wants to build one (with parts available here!)