I'm not chastising your for lacking knowledge and experience with electronics, nobody can know everything :) I just want you to think about your limitations, and keep in mind that estim hardware is potentially dangerous stuff even when working as intended. An estim device takes a weak harmless signal and amplifies it, then it boosts the voltage with the transformers. High voltage AC signals are dangerous. Estim signals aren't super high voltage but still enough to pose some dangers.Dabow wrote: ↑Wed Apr 17, 2024 4:37 pm I'm sorry. I'm definitely the knows enough to be dangerous type of person, which is why I'm asking a lot of questions before I begin. I want to make sure I understand what I'm doing any why I'm doing it. I'm following the low cost (~$40-50) build linked below, but that build does not have a left and right volume built into it.
viewtopic.php?f=12&t=23322
I can look at the part/schematics, look at other builds, and figure it out but I definitely wanted to know where this went and if it mattered. The volume potentiometers are one thing that was hanging me up. In my mind my card already had the single input and I hadn't even considered making my own left and right input going into my box, volume, then back to the single input. Hard to break out of the box I had created for myself in my head. For now I will not have the parts to complete my build with left and right volume control. My amp has the 3.5 mm input as well as bluetooth connectivity. I live in a rural area so hopping in the car and going into town is a 25 minute drive. I should be able to grab what I need when I go next. Until then I should be able to put my build together as outlined in the low cost build linked above and at least test it out.
The building your own DIY estim linked below is what confused me about grounding. I was looking at it trying to figure out what I was doing with the separate channel volume and saw that it had wire labeled ground, which I did not have the ability to wire to my board. It makes sense that it all goes into the 3.5 mm jack like you linked.
viewtopic.php?t=23302
All of the responses sure clear up the confusion I had lol. I guess saying something dangerous elicited some good responses. Thank you everybody for the help.
Here are some example scenarios which could cause the estim current to pass through your heart and respiratory tract:
- You haven't read the estim safety guides, and connected electrodes to your nipples.
- One of the electrodes come off your body, causing the signal to stop completely, and you grab it with your hand to reattach it without turning off the device.
- An unshielded wire inside the box comes loose and touches a metal part inside your box, causing either the casing, connectors or volume controls to get electrified.
- Some estim mp3 has low amplitude and/or high frequency so you turn up the hardware volume to a nice level, then your mp3 player automatically switches to the next track which gets played at a very high intensity.. Or you accidentally brush against the hardware volume control and raise the volume.. So you get a mild panic and grab the electrodes with your hands (I've had similar things happen due to software issues, and I can tell you that it's very difficult to move the mouse pointer to click a small stop button while you're being zapped :D)
Now, a young and healthy individual will likely survive this, but you might not know that you have a weak heart until it becomes a problem. Unless you have someone nearby who can perform CPR until the ambulance arrives, this probably means certain death.
To make it more dangerous, stronger estim signals are capable of triggering muscle contractions. The signals don't even need to be so strong that you perceive them as painful. But if you fully grab something electrified then you might find yourself unable to open your hand and let go of it. I would guess that normal estim signals aren't strong enough to also cause full body spasms if this happens, so hopefully you'll be able to pull your whole body away and unplug some banana connector or use your other hand to hit the power switch. Again, if you're healthy I don't think there's a huge risk of cardiac arrest even if the current passes through your torso, but it's still not something I'd want happening to me :)
In really worst case scenario, you've bought the cheapest and most unreliable components from amazon/aliexpress/wish, the power supply suffers a catastropic failure and the mains voltage burns through to the amplifier. The amplifier, built to handle 12-24V DC, has no way to stop a sudden 120/230V AC current and it passes on the speaker outputs. The already dangerous mains voltage gets further boosted by the transformers, either instantly killing you or only blowing your dick off, depending on the path it takes through your body. I think this has extremely low probability, even with the cheapest components, but the consequences would be pretty severe. Though hopefully you've bought both power supply and amplifier with fuses.
There's another DIY electronics project involving AC and transformers called fractal wood burning, which of course is much much more dangerous than e-stim since it works with higher voltages and currents. But if you want some healthy respect for DIY electronics and high voltage AC in general, I think this is a pretty good video: https://youtu.be/wzosDKcXQ0I?feature=shared&t=441
It's of course all up to you, so these are just my recommendations:
- In your original schematics, draw a vertical line down the middle of the amplifier. Everything to the right of this line is potentially dangerous and do not make any modifications to these parts. I.e. basically the transformers and both the wires going into and out from them. Don't fuck around with the power supply either (or try to use one with higher voltage than what the amp is rated for) but I suppose adding a power switch to the supply voltage might be a good idea if there isn't one already.
- Buy shrink tube and insulate all cable/cable and cable/resistor joints as a safety precaution. Electrical tape might work but at least the cheap kind has a tendency to fall off after some time.
- Place the electronics in a plastic or wooden box. Make sure all connectors (jacks, alligator clips, or whatever you decide to use) are fully insulated and don't have metal casings etc.
- If building DIY electrodes, make sure only the parts touching your skin are conductive if possible. E.g. a conductive rubber loop might be impossible to insulate, but if you build something out of a stainless steel jigger then at least cover the outside with electrical tape.
- When using the box make it a habit to always both turn off the power and/or turn down the volume if you need to adjust the electrodes.
The volume control is a "safe" project as long as you put it on the signal going in to the amplifier (the 3.5mm jack is on the left side of the vertical line I mentioned before :)) The post you linked does not say "ground" as far as I can see, but it has a link to a different post with version 2 of the same thing, which IMO is better drawn. viewtopic.php?p=326644#p326644
The updated drawing does say ground (GND) but this is just the audio signal ground/common. You should not think about connecting this to anything else in order to further ground it if you were doing that. The 3.5mm audio input on your amplifier has 3 connectors internally: left, right and GND. The version 2 drawing including volume controls has 3 lines going into the amp, so this should be exactly the same as yours if I understand you right. If you buy a 3.5mm audio plug with cable, like the one I linked to on aliexpress, then you'll get an easy way to connect the two potentiometers.
You can of course also try to DIY your own 3.5mm audio plug/cable. If you have a cable and cut it, it might have left and right as 2 different colored shielded wires in the center, surrounded by multiple strands of unshielded copper which is used for GND instead of a third wire.
