There seems to be a strange background noise on my Touch Board - like a crackle/whistle sound.

The Touch Board goes through a rigorous testing procedure, however there can occasionally be manufacturing issues or errors, if you hear a background noise this can be a sign of an error in the manufacture of your Touch Board.  If you have any problems with the Touch Board straight out of the box and you’ve been through all of the above step to verify it does not work correctly please get in touch and we can arrange a replacement.

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    Wesley Swafford

    Actually, I found that this can be caused by using an unshielded audio cable right next to the power cable as well. I have a Bluetooth speaker / external battery, and when I tried to both power the TouchBoard from it, and use it for audio, I got the same crackling / whistling sound described here. When I powered it from another source, or used headphones, it was clear.

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    Bare Conductive

    Thanks Wesley, good to know this can also be the cause

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    Ken Zemach

    Like Wesley, I've found the same thing. I was trying to build a small project box which contains both a small speaker and the touchboard (and an I/O connector, etc). I wanted to have a single on/off switch and just power everything from the speaker battery. No luck! Whether it be a shielding issue as noted by Wesley, or a feedback loop via the speaker audio connector being on the same ground as the power ground, I dunno, but it just sounds horrible. I'm going to have to add a second battery; that in itself isn't that hard, but doing a remote on/off switch for the Touchboard SEEMS to be difficult as the current hard wired one is double pole, switching the center lead from ground to power. That's problematic, as the way I'd like to handle it is to have the single on/off switch simply shunt +5V to the center lead by the switch when on. THAT will work, but then when turning the entire system off, that center lead isn't swapped back to ground. So now, handling the charging of that independent battery becomes an issue when also charging the other independent battery in the speaker. I THINK what I'll do is probably do a DPDT switch instead, and when in the "off" position, connect the two batteries in parallel so they both charge together, but in the "on" position separate them and shunt the 5V power to the board (and leave the hard switch on).

    The only theoretical, albeit probably not practical, problem with this approach is that IF one of the two cells gets drained a lot faster, then when turning the system off and putting the two batteries in parallel, there is no current control on the ability of one of the batteries to instantly try to charge the other which is not really either proper or safe. it won't overcharge, because the other battery can't be over overvoltage, but the rate at which it charges might be improper.

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    Bare Conductive

    Hi Ken

    Your comment is quite long and involved, so if you would like to email us at it may be easiest for us to help you there.

    However, I'm not quite sure what you're trying to achieve here or how best to help. The Touch Board can be powered via a 5V USB source or via a 3.7V Lithium Polymer cell connected to the 2-pin JST PH connector near the bottom left of the board. Without a schematic or drawing it's hard to quite picture how you might power the board from a battery within a small speaker - if you could email over photos and drawings that would help.

    If the speaker has a USB input socket for power / charging, you might use a USB battery pack with two outputs - one powering the speaker, the other the Touch Board.

    The power switch on the Touch Board controls the enable pin of the onboard boost regulator - as you rightly say, one pole of the DPDT throws between VIN and GND - you can take a look at the schematic here: file:///Users/owner/Downloads/touch-board-kickstarter-edition-schematic.pdf. If you want to switch the board on or off remotely, I would do so by switching the USB input power.

    The one bit of hard advice I would offer is never to charge unmatched Lithium Polymer cells in parallel. Any voltage mismatch can result in significant current draw which can damage the cells, often with pyrotechnic results.

    If you can provide me with a more clear idea of what you're trying to achieve I am sure that we can help you come up with an appropriate solution.