DIY Optical Hi-Hat sensor

If you need a Hi-Hat sensor here is a simple PCB to build one yourself.

• 1. DIY Optical Hi-Hat sensor
     • 1.1. Schematics
     • 1.2. Bill of material (BOM)
     • 1.3. Connector
     • 1.4. Adjust IR brightness and sensitivity

Assembly

The core of the PCB is a cheap TCRT5000 Infrared Reflectance Sensor.

• For the lower part use a 13” Low-Volume Cymbal. You may want to put a rubber rim on it, to reduce the noise.
• For the upper part use a 14” (rubber) Cymbal Pad.
• You will need a reflector on the top cymbal right above the IR sensor to reflect the light.
  • If you can get a reflector of a “real” e-Hi-Hat like the one in the picture above, go for it.
  • A plastic disc with a diameter of 4 cm and black electrical tape on it will probably work too. Put a hole in the middle so that you can screw it onto the Hi-Hat clamp.
    • Make sure the disc is not too reflective (i.e. do not use a CD or a mirror).

Schematics

All files that you need to order your Hi-Hat Sensor PCB (GERBER file, …) are here.

Bill of material (BOM)

Component	Designator	Quantity	Price / Unit	Price Total	Comment
Potentiometer 5k	R1	1	0.35€	0.35€	Supports Piher PT10 (10mm) / PT6 (6mm) or Bourns TC33 (SMD)
Resistor 100 Ohms	R2	1	0.03€	0.03€	THT or SMD 0805 package, 125mW (or 250mW), 1% or 5%
n/c	R3	0	-	-	Not required, as the EavesDrum module already has a pull-up resistor (R11) on it’s ADC2 input
TCRT5000	U1	1	0.30€	0.30€
3-Pin Header (male)	J1	1	0.09€	0.09€
PCB	-	1	~4€*	~4€*	* Example for 5 PCBs at JLCPCB excl. Shipping/Tax. Shipping/Tax is approx. 2.50€ (Global Direct) or 7.50€
Total				24.66€

If you search for a shop for the TCRT5000 and are located in Germany you might want to take a look at BerryBase.

Connector

Pin	Function	Comment
1	GND	Connect to the GND of the EavesDrum Trigger Module. Usually the shield / metal housing of the SUB-D37 connector
2	OUT	Sensor output. Connect to the ADC2 pin of the EavesDrum Trigger Module
3	VCC	Supply Voltage (3.3 or 5V) for the IR LED. Connect to hh_vcc of the EavesDrum Trigger Module

Adjust IR brightness and sensitivity

You can adjust the brightness of the IR LED as well as the sensitivity of the IR sensor.

For the brightness:

• The Supply voltage of the hh_vcc output of the EavesDrum Trigger Module can be switched by the jumper / slide switch JP6 between 3.3V and 5V.
  • Both should be fine but the IR LED brightness will be higher with 5V.
• You can also regulate the brightness with the potentiometer R1 on the Hi-Hat sensor module. You can see the brightness of the IR LED with your smartphone camera (as long as it does not have an IR filter).
• It is best to open the EavesDrum drum UI and monitor the Hi-Hat Pedal. This way you can adjust the brightness of the IR LED easily.
  • Just make sure that the signal uses most of the range between 0% and 100%.
  • If the level is near the closed level even when the Hi-Hat is fully opened: decrease the brightness.
  • If the level is near 0% even when the Hi-Hat is fully closed: increase the brightness.

For the sensitivity:

• Use potentiometer R11 on the EavesDrum Trigger Module. Simply turn it to the center position. This will probably be good enough.