Hi everyone,
I have a WAV Trigger rigged up with four AT42QT touch sensors triggering various sounds, and it’s working well but I’d like to add a short analog LED strip that lights up when any of the sensors are activated. I’m attempting to use the LED pin of each sensor to set the digital input on an Arduino pin HIGH, and I got that to work with one sensor, but my uncertainties have to do with power consumption for all devices running off 1 power supply. I have an IRLB8721 mosfet chip that I would use for the LED strip, but still unsure of how to power everything else.
How might I calculate voltage and current for all the devices? Is it better to power the Arduino off of the WAV trigger or vice versa? Does it even matter? I can post pictures of the circuit if that would be helpful.
Thanks in advance for your guidance!
Thanks for the question!
The Arduino and touch sensors combined are not going to use too much current. Probably less that 75mA combined, but you would need to stick a ammeter in series with your power source and the assembly to know for sure. Not sure how large your LED strip is or how much current it needs, but if it’s small and not super bright and doesn’t get hot when it runs, it probably doesn’t need much current either. (Maybe a few hundred mA max?)
What are you using for a power source? What voltage does it provide and how much current can it deliver?
If you post a picture of what you’re working with, we could probably give you some pointers, but it sounds like you could use the same power source to run everything. Worst case, you run the Arduino touch sensors and WAV Trigger from one power source and the LEDs from a second.
Not sure which power source yet but I’m leaning towards a 12v 600mA wall plug with barrel jack because I might use one of these 1-meter long analog LED strips:
https://www.sparkfun.com/products/12021
I wonder if there’s a way to forgo using an Arduino to control the strip and use the WAV trigger instead? Or does it not have the capability to control a strip of LEDs? I’m able to turn a single LED one with the output from the LED pin of the touch sensors, but no more than just the one.
The WAV Trigger itself can’t control LEDs, but depending on what you want the LEDs to do, you may be able to tap into that LED pin on the touch sensor and have that turn on a MOSFET. The MOSFET would then switch on your LED strip. The strip will only be on as long as your touching though.
If you wanted the LEDs to anything else, you’re going to need some sort of logic that instructs them how to behave. Arduino would probably be the easiest route to go, but other micro controllers or even a bunch of digital logic could be used.
For power, a 1m LED strip is going to need a lot of it. Each color needs 1.2A of current and there’s three colors in the strip you’re wanting to use. Unless you cut the strip shorter, you’re going to need at least 1.2A and up to 3.6A of current just for the LEDs. a 600mA power pack isn’t going to be enough to run the LEDs let alone the LEDs and WAV Trigger together. A 4-5 amp power supply like TOL-14934 would be ideal if you want to light the whole strip and have power available for other things. To be honest, you’re probably better off using a small power supply for just the WAV Trigger and touch sensors and then using a second larger supply for just the LEDs.
That works! But only with 1 touch sensor connected to the MOSFET. Is there a way to activate the MOSFET with any of the 4 touch sensors ? I had connected them all to one row and took a wire out of that row into the MOSFET, but then none of them work.
My goal is to activate the LEDs just the way you described (on or off with touch and that’s it) and the same set of LEDs lights up by touching any of the 4 sensors.
OK, what’s probably happening is the output from the active touch sensor is feeding back into the inactive touch sensors and shorting out. I haven’t tested this, but I think if you construct a simple OR gate with some diodes, you should be OK. Give the circuit in the photo below a try.
I will try it! Thank you thank you
It works perfectly! Thank you so much for the help!!!
No problem! Glad I was able to help.
Happy hacking!
Oof, one more little thing I’m uncertain of -
I’m using a 12 v 500mA wall wart to power the WAV trigger, but it seems to only be able to send 3.3 or 5 volts at its 8-pin output set (the ones next to the FTDI pins).
What’s the best way to pass the 12 volts/500 milliamps through to the rest of my circuit? I see there’s a V-IN and GND pins between the power port and SD port, will that suffice?
Yes, VIN and GND are connected directly to the barrel jack and whatever voltage you’re applying to the jack will show up there. That would be a good place to pickup 12 volts.
I hooked that all up and broke the WAV trigger 
Not sure what I did wrote, I checked and double-checked my connections and everything is exactly the way it was in my prototype except for I was only sending 3.3v before. I should have tried 5v first… I’m not sure if the WAV trigger can really transfer more than 5v to external circuits?
Looking at this info page, it seems like it’s a “no” based on the first section:
https://robertsonics.com/wav-trigger-on … /#chapter1
If you’re just trying to pull 12 volts via the barrel jack from VIN and GND, that shouldn’t have broken anything.
Depending on how much current you’re trying to pull from the 3.3V and 5V pads, that could cause you to burn out a voltage regulator. Also, if any voltage back fed into the 3.3V or 5V lines, that could also damage the WAV Trigger. I don’t know what your circuit looks like so I can’t say what caused the issue, but it might be better to not use the 3.3V and 5V outputs from the WAV trigger and use another voltage regulator on your 12 volt line to drop that down for the rest of your circuitry.
I have a circuit all wired up and it works for a short time and then start acting glitchy. I think the issue is with the Sparkfun touch sensors. Two of the sensors seem dysfunctional now and I wired up two new ones. It seems to work at first but I’m getting some stray current it seems. I’m thinking I need to add some current-limiting resistors but I’m not entirely sure where.
Here’s a run-down of what’s all connected:
Power supply is 9v / 500mA positive center pin
WAV trigger connected to four AT42QT capacitive touch sensors (by Sparkfun)
5v output and ground rails → VDD and GND of touch sensors
OUT pins of touch sensors → T1 thru T4 of WAV trigger
LED portion:
Touch sensors’ LED-out pins each connected separately through a 1N4148 diode into gate pin of IRLB8721 mosfet
Drain pin of mosfet out to cathode pins of 5 green LED’s and tied to ground through a 10k resistor
Source pin connected to ground
5v from WAV trigger connected to anodes of LED’s each through 270 ohm resistors
I made a short video of the glitches I’m seeing, here’s a link:
https://www.youtube.com/watch?v=FHdmIaIjw1w
I can post more pictures of the circuit if the above description is not clear enough or confusing? I could also attempt to make a proper schematic 
I’m not sure what’s going on there.
Can you supply a schematic so we can see the exact circuit you’re using?
What happens if you disconnect the WAV Trigger from the sensors and just power those with 5 volts?
Here are 2 drawings illustrating the schematic. The first picture shows the connections between the WAV trigger and the touch sensors (not including the LED pins of each sensor - that is on pic #2 which hopefully will transmit even though it’s not letting me add it as an attachment for some reason)
Apologies for the rudimentary quality, I don’t have proper schematic-making software!
For some reason I am not able to post a photo of the 2nd schematic picture. Grrr… I even re-took the photo and it STILL won’t let me. Is there an easier way to share photos?
There we go. Okay so this is the LED circuit using an IRLB8721 MOSFET and running each out pin through a diode at your recommendation. The whole kebab works for a short time and starts glitching out after not very long. What happens is the touch sensors begin triggering on their own. I thought using the diodes would help that but perhaps I need a different diode?
I really can’t say for sure what’s causing this, but my theory is your LEDs are drawing more current that the 5 volt rail on the WAV Trigger can supply. The symptoms you’re describing sound like the regulator heats up due to excessive current then begins cycling on and off to reduce heat. I think that’s what’s causing the glitchy behavior of your touch sensors.
I’d recommend trying the sensors and LEDs on their own separate 5 volt power supply and see if that does the trick. You would need to connect the ground (negative)on both power supplies though.
I think the problem lies with the touch sensors because I removed the entire MOSFET + LED portion of the circuit and still seeing glitchy behavior on the touch sensors where they are constantly triggering some kind of sound. As soon as a sound clip finishes, all 4 sensors light up and trigger a sound until there’s no sound being played, and they light up and trigger again without any touch input. I tested the entire proto board for shorts and found zero…
A few things I’ve noticed is the touch sensors activate on lift-up instead of touchdown. So there’s been some kind of polarity inversion… or I guess they need pull-down resistors but I didn’t have to do that in the past with these sensors. Also when I’m not touching the sensors, they are dimly flickering.
I’m very confused 
I did rig up the MOSFET + LED circuit on its own proto board with an Arduino Uno and am using a very basic code to fade the LED array up and down. This was just to be sure that portion of the circuit was indeed working.
