Imported from GitHub: jwnimmer/upiez · commit 8681305 · license CC0-1.0

Description

Piezo sensor triggering a LED strip

README

https://github.com/user-attachments/assets/209be3a4-444d-4c55-9051-d0b7a3d1a6b6

upiez

The upiez is a printed circuit board with a piezoelectric sensor input to detect vibration (e.g., when a drum head is hit), and when a strong enough vibration is sensed it switches on its power output (e.g., lighting up a LED strip) for a configurable, short amount of time.

The board accepts an input voltage from 4V to 20V, and can power up to a 3A load. The input voltage should match whatever is used by the load (LED strip) -- it does not regulate the output, it only switches the power on and off.

The board offers two trimmers for adjustment -- one trimmer to adjust the piezo input sensitivity trigger, and one trimmer to adjust the time the LED stays illuminated after each trigger.

Connectors:

• LED output is on a 5.5/2.1mm barrel jack (PJ-063AH) at J1.
• Piezo input is on a 2-pin header (0.100" pitch) at J2.
• Power input is on solder pads for hard-wiring (on the bottom).

Size:

• PCB 28.2mm x 20.3mm (not including connector overhang).
• Mounting hole spacing 23.1mm x 15.2mm for M2.5 screws.

Designed summer 2024 for the LWHS drum line.

This project requires wire stripping and soldering skills, and ideally a multi-meter.

For an easier starting point, see also the (TBD link) breadboard version of this project.

Theory of operation

• Power regulation for the internal components:
  • Input power comes in on the J3 and J4 pads.
  • U2 regulates the power down to 3.3V for use by the internal components, with C1 and C2 for filtering.
  • D1 illuminates to indicate suitable power input (at ~4mA per the 2V LED drop and 330 ohm R1).
• Piezoelectric sensor input:
  • An external piezo sensor harness is connected to J2.
  • For the purposes of this exposition, treat the sensor as a current source.
  • When current is input via J2, it develops a voltage across VR1 pins 1,3.
  • The user's setting of the VR1 trimmer divides that voltage onto VR1 pin 2, which feeds the N-type MOSFET gate at Q1 pin 1.
  • Q1 provides ESD protection on its gate, so if (when) the voltage developed across the trimmer goes too positive or too negative it shunts the current to ground.
    • I've seen other projects use a dedicated protection diode for this, but relying on the ESD protection saves us on part count and seems to work OK so far.
  • When the gate voltage goes high enough, Q1 turns on (connecting pins 2 and 3), thus pulling U1's pin 2 ("trigger") low. (The 555 trigger input is active-low.)
    • With no piezo input, U1 pin 2 is pulled high by VR2.
      • This is a little trick to save on part count. By putting the 3.3V on the middle pin of the VR2 trimmer, we can use half of the part (pins 1 and 2) for the RC timer (described below) and the other half (pins 2 and 3) as a pull-up resistor for the trigger. The pull up will have an arbitrary resistance (>= 1k ohm) but that doesn't matter.
• Timer:
  • U2 is a CMOS 555 timer configured in the classic Monostable mode.
    • The decoupling capacitor C4 is normally supposed to be a 100x smaller value (higher frequency response), but I decided it didn't matter enough to increase the unique part count.
  • In the RC circuit we have a fixed 1uF capacitor with a variable VR2 trimmer (1k..99k ohm).
    • This allows for a range of timer output between 1-108 milliseconds.
    • For reference, at a tempo of 144 a sixteenth note is 104 milliseconds.
• Output stage:
  • When the timer output (pin 3) goes high:
    • D2 illuminates; this is helpful for debugging.
    • Q2 turns on (connecting pins 2 and 3), thus providing a ground for the barrel jack J1's negative terminal.
      • The barrel jack J1's positive terminal is always connected to the VDC power input.
      • In other words, we turn the LED output on and off by connecting and disconnting its ground, not VDC.

Single channel version

This is the single channel assembly for use with a single sensor, e.g., a snare drum or bass drum.

The upiez PCB must be externally powered, using a power source voltage that matches the voltage of the LED strip. For my build, we used this 12V LED strip so our power source must be 12V.

When choosing a LED strip, also consider how much current it needs. According to a review comment on that product, the full 5 meter length uses 1.94 amps @ 12 volts = 23 watts. The max current of the upiez is 3 amps, so the 1.94 amps is safely within the limit.

In our case, we never put a full 5 meters of lights on a single drum anyway. That would be a lot! We only wrapped the rim of the drum head, so approx 1 meter for snares or 2 meters for a large bass drum. The LED strip can easily be cut into segments for the necessary lengths.

This brings the power requirements down into a regime where a 9V battery can handle the load, we just need to boost it from 9V to 12V. For that, we used these DC-DC boost modules. Checking the ballpark math: 2 meters of LED is ~9 watts, which we source as ~9V @ ~1A. Typical sustained current from a 9V cell is around 1A with burst around 2A, so the math checks out okay.

Another way to get to 12V would be with an 8-pack of AA or AAA batteries, to avoid the need for the boost converter. I never tried this, because I am somewhat skeptical it would work well -- as you use the 1.5V batteries, their voltage droops pretty quickly to the point where your 12V supply is now 11V or 10V, and that reaches the point where your LEDs will get dim and then stop working entirely -- there is a minimum voltage floor required to illuminate all of the diodes, and it's in that neighborhood. Also the 8-pack is larger and heavier than the single 9V. Using the boost converter ensures consistent brightness so long as the battery has any juice left at all.

Single channel version: assembly details

The DC-DC boost module linked above has a trimmer to adjust its output voltage. Before wiring it to the upiez you MUST connect it to a load (e.g., 1k resistor) and supply (9V battery) and adjust its trimmer until the output is 12V on your multimeter. If its trimmer is in the wrong position, the boost module can output up to 35V which is enough to fry the upiez (max 20V).

To turn the kit on and off, instead of (un)plugging the battery we found it a lot easier to install a rocker switch as part of the battery harness. Then the battery can stay plugged in, but still power off the kit easily.

It's best to test each component by itself (the upiez and boost board) before starting to wire them up.

This photo shows how we chose to assemble the 1-channel kit:

• On the "inner" side of each of the two boards in the stack, cover metal surfaces with kapton tape to prevent a short circuit.
• Use ~3 pieces of double-sided tape as a spacer under each of the two screw holes on the side of the upiez with the small green LEDs (D1 & D2, top of photo).
• Use the following mechanical fasteners (near C4, bottom right in photo) to attach across a mounting hole in each of the two boards:
  • 91292A014 18-8 Stainless Steel Socket Head Screw, M2.5 x 0.45 mm Thread, 10 mm Long, Packs of 100
  • 94669A094 Aluminum Unthreaded Spacer, 4.500 mm OD, 3 mm Long, for M2.5 Screw Size
  • 91828A113 18-8 Stainless Steel Hex Nut, M2.5 x 0.45 mm Thread, Packs of 100
  • 90940A102 Polycarbonate Plastic Washer for M2.5 Screw Size, 2.7 mm ID, 5.0 mm OD, Packs of 25

Quad channel version

A single-channel version of upiez is great, but in a pinch it could be built on a breadboard instead (see link TBD). The raison d'être for upiez is multi-channel operation. (Building a 4- or 6-channel version on a breadboard is not very practical.)

We designed upiez to use right-angle connectors and to match the footprint of the Adafruit 5991 USB-C power board, so that we can stack modules for multi-channel operation. The 5991 offers DIP switches to select an output voltage (5-20V). The important point is to also choose a USB-C PD source that is compatible with the voltage you need. We used the Anker Nano Power Bank 30W which can handle many output voltages. There are probably cheaper options, but the quality and usability of Anker products is top notch and now we have a good power bank to use on vacations as well.

Adafruit 5991	Anker Nano

Quad channel version: assembly details

Gather all of the parts before starting. That includes having upiez boards fully finished -- the two connectors soldered on, and the power wires soldered onto the bottom of the board.

It's best to test each component by itself (the upiez and power board) before starting to wire them up.

• Use the following mechanical fasteners (required quantities listed are pieces, not packs):
  • 4x 93805A120 18-8 Stainless Steel Threaded Rod, M2.5 x 0.45 mm Thread Size, 50 mm Long, Packs of 10
  • 8x 91828A113 18-8 Stainless Steel Hex Nut, M2.5 x 0.45 mm Thread, Packs of 100
  • 12x 94669A104 Aluminum Unthreaded Spacer, 4.500 mm OD, 10 mm Long, for M2.5 Screw Size
  • 4x 94669A094 Aluminum Unthreaded Spacer, 4.500 mm OD, 3 mm Long, for M2.5 Screw Size
  • 40x 90940A102 Polycarbonate Plastic Washer for M2.5 Screw Size, 2.7 mm ID, 5.0 mm OD, Packs of 25

Cover the top of the barrel connector with a little kapton tape, just to make sure it doesn't short onto the board above it. There should be enough clearance, but if you have a large blob of solder on the bottom of the nearby board there might be contact.

I started from the USB board and worked my way up. It's probably fine either way. Use a washer under every nut. I also used washers on both sides of each spacer (thus the 40x washers shown above), but that was probably overkill. One washer per spacer should be enough to separate the boards so they don't short, and would save some money. Finish fitting all four bolts' worth of fasteners before using any tools to start tightening. Tighten each of the four corners a little bit at a time, to keep everything squared up.

PCB assembly

We ordered the boards from PcbWay, including SMT component sourcing and assembly. Because of the small size of the board, it is processed and shipped as panelized (2 x 2) with break-away rails (so must be ordered in multiples of 4). The first step for finishing up the assembly is to carefully break all of the board off of their rails.

After that, hand solder the connectors:

• J1 is Cui PJ-063AH
  • Mount on the top of the board, solder from the bottom.
• J2 is Harwin M20-9950245
  • N.B. This connector part number is a 2x2 header, but we need a 1x2 header. Carefully cut the connector in half. (Buy spares since you'll probably break some accidentally.)
  • Mount on the top of the board, solder from the bottom and then flip back to the top to touch up with some extra solder.
  • If you are building a single-channel board and don't care about the right angle header, you can use any cheap 0.100" pitch pin header instead. The piezo harness will exit from the top of the board so will be less ergonomic to use, but if you already have 0.100" pin headers lying around will be easier and cheaper to solder up.
• VDC and GND are on solder pads on the bottom of the board, for wires.
  • For me, soldering in the 22 AWG stranded 2-conductor cable was easier than solid wires.
  • Note that each of the two the pads is right next to a through-hole pin on the same circuit, so it's OK for the wire solder to join up with the through-hole solder. The dashed line indicates the terminals that are all the same (one for VDC, one for GND).

In our first build we soldered J1 then J2 then the wires. This ended up being somewhat of a headache because J1 is very thoroughly connected to the board's ground plane and its metal shield, so the ground pin of J2 and the GND wire both struggled to flow evenly with the iron we used due to heat leaking away quickly. Next time, we should probably solder J1's shield pins last.

Harnesses

Piezo harness

The upiez piezo input is on J2, via a standard 0.100" 2-pin header. There are many ways to wire up a cable to this, I'll detail the one I used:

• Use pre-made Female Breadboard Jumper Wires 2.54mm for the cable end that connects to upiez.
  • Peel off a pair of two wires, and then cut the jumper in half (so one end is connectorized and the other end is wire leads).
• Use 22 AWG stranded 2-conductor cable for the long cable run.
• Use 1" piezo sensor with with leads for the sensor at the end of the cable.
  • Add dabs of hot glue on the piezo discs to secure the tips of the wires to the metal. The connections from the piezo wire leads to the solder blobs on the piezo discs are the weakest link and will break off unless you reinforce it with glue.
• Prepare and stage appropriately sized heat shrink on all of the wires / cables.
  • Use a small piece on the red (positive) joints, to prevent shorting to the nearby ground joint.
  • Wrapping the black (negative) joints is also fine but probably not necessary.
  • Use a larger piece around the whole cable at the joint, for mechanical stress relief.
• Strip the ends of wires as necessary, solder the connections, slide the heat shrink into place and shrink it.

LED harness

This is the simplest of the harnesses. Your LED strip might already come with barrel connector(s) built-in. If not, buy a pack of 5.5mm/2.1mm "male" barrel jacks with leads and solder to your LED strip(s). For example, here are jacks with 20-inch leads, or if you need longer try something like double-ended 10' cables and cut them in half. For stress relief, cover the LED-wire joint with heat shrink tubing.

Single channel power / battery

This explains the power wiring for the single-channel example. The goal is to connect a 9V battery to the boost converter with an inline switch.

Example parts list:

• 9V battery clip with wire leads.
• Automotive rocker switch, pre-wired
• 22 AWG stranded 2-conductor cable

The switch breaks the connection betewen the battery and the input to the boost board. It works equally well breaking either the positive or negative connection.

Example with the switch on negative connection, matching in the picture above:

• Solder one end of the 2-conductor cable to the battery leads (red to red, black to black).
  • Use heat shrink similarly to the piezo harness, above.
• On the other end of the 2-conductor cable:
  • Solder red to the "IN +" hole on the boost board.
  • Solder black to one of the switch's leads.
  • Solder the other lead to the "IN -" hold on the boost board.

I used the same stranded 2-conductor cable to connect the "OUT +" and "OUT -" from the boost board to the VDC and GND pads on the upiez. Remember to adjust the boost board voltage output before connecting it to the upiez.

Quad channel power pigtails

For the stack-up of 4 piez and the 1 adafruit USB-C board, I used the following procedure for power wiring:

• Solder red and black wires onto each upiez. Be sure to have them pointing in the direction you want for the stack-up (probably the same side as the Adafruit terminal block).
• Assemble the stack with screws, bolts, spacers, washers, etc.
• Cut one of pair of red and black wires and attach to the termin block on the Adafruit.
• Gather all 5 wires of each color into a pigtail.
• Zip tie the wires onto the spacers to avoid fatigue.
• Solder each pigtail and cover with heat shirink.

I used solid hookup wire when I did this, which ended up being bit too stiff. Next time, I'd try the same stranded 2-conductor cable used everywhere else.

Mechanical drawing

Costs

Here's the approximate part costs as of 2024. Costs shown are all per-item, based on qty 20 purchase.

Item	Cost (USD)	1-channel qty	4-channel qty
upiez board (assembled)	6.35	1	4
Piezo harness	2.00	1	4
LED harness	1.00	1	4
HiLetgo XL6009 DC-DC boost	1.90	1
9V battery harness	1.50	1
1-channel fasteners	1.15	1
Adafruit 5991 USB-C power	9.95		1
4-channel fasteners	25.65		1

Nearly half of the fasteners cost is from the washers. In retrospect, I should have selected a cheaper part number, or omitted the washers.

For the 1-channel assembly, total cost is 6.35 + 2.00 + 1.00 + 1.90 + 1.50 + 1.15 = $13.90 (plus the cost of the LED strip and 9V battery).

For the 4-channel assembly, total cost is 4 * (6.35 + 2.00 + 1.00) + 9.95 + 25.65 = $73.00 (plus the cost of the LED strips and the USB-C battery).

upiez cost detail

Item	Cost (USD)
Board (unpopulated)	1.14
SMT components	2.26
SMT assembly	1.50
THT components	1.45
THT assembly	0.00 (self)

Credits

Reading other people's take on this kind of project was a great help in my own design. My primary sources were:

• Davide Gironi: https://davidegironi.blogspot.com/2014/06/drum-light-trigger-that-uses-leds-ne555.html
• Sam vs Sound: https://samvssound.com/2017/11/24/555-based-piezo-trigger/

Thanks to KiCAD EDA.