Hair electrolysis machine hardware

Read the blog post: https://www.scd31.com/posts/diy-hair-electrolysis-machine/

Check out the firmware: https://gitlab.scd31.com/sophie/hair-electrolysis-machine-software

This is my DIY galvanic hair electrolysis machine. It's able to generate ~15V at a programmable current (up to around 2.5mA limited by the actual hardware), which is more than enough to permanently kill hair follicles.

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Disclaimer

I am not an expert or a doctor or anything. Definitely assume everything here is wrong and do not reproduce this project unless you know what you're doing. Electricity can do some damage to your body, and overdoing the lye can cause scarring.

How hair electrolysis works

Hair electrolysis involves running a small current (around 1mA) through your body via two electrodes. One electrode is inserted into the follicle and the other is placed somewhere else on the body. The polarity is positive on the outer electrode and negative in the follicle. This forms an electrolysis cell with your body as the electrolyte, such that a small amount of sodium hydroxide (lye) is generated in the follicle. Hydrochloric acid is generated at the other electrode, although it's in such small quantities and over such a a large area that this is safe. [Obligatory reminder that I do not know what I'm talking about]

The sodium hydroxide is very basic, and permanently kills the follicle. At this point the hair can be removed with tweezers; if done properly, there should be almost no resistance.

Basically the only factor to control is the amount of lye generated. More lye can kill larger follicles, but too much lye can potentially lead to scarring (although my understanding is you have to really overdue it. I have not run into this myself).

The amount of lye generated is just the time integral of current. 1mA for 1s produces 10 units of lye. More current hurts more, but less current takes longer, so it's all about striking a balance. Here are some target values of lye I found in a textbook:

Hair type	Amount of lye (LU)
Fine, unpigmented vellus hair	10 - 15
Fine, pigmented, soft hair	10 - 20
Medium/shallow terminal hair	15 - 30
Deep terminal hair	30 - 45
Very deep terminal hair	45 - 60

In practice these numbers are pretty lose and I've heard of people needing much more or much less lye. Experimentation is required.

How this board is used

The board is able to self-test itself via the main menu. This is strongly recommended to make sure the charge pump is working and the current DAC able to set current accurately. I normally run this every time I boot up the board.

The hair removal procedure is as follows:

1. Use the settings menu to set the maximum current, ramp-up time (otherwise known as the current slew rate), and total lye required. This will be stored in flash. You may need to adjust these settings over time, especially when moving to larger or smaller follicles.
2. From the main menu, go to "Start".
3. Insert the needle into the follicle.
4. Press the foot pedal. You'll feel the current ramp up over time. On the screen, you can verify that current is being delivered. 4a. The lye acts as a lubricant and makes it a lot easier to slide the needle. This makes it easy to adjust if needed. There's definitely experimentation to be had here.
5. When the target amount of lye is reached, the current will stop. This is preferable to taking your foot off the pedal, as the instant current change is quite uncomfortable. The target lye end condition includes a ramp-down period which feels much better.
6. Pull out the hair with a pair of tweezers. This shouldn't hurt at all and it should basically just fall out. If there's resistance, you may need more lye. Be careful though, because too much lye can cause scarring.
7. Go back to step 3, until you're out of follicles (:

BOM

A BOM of LCSC components is generated as part of CI/CD, and is available here. Aside from that, there are several things you'll need:

Name	Purpose
F4 electrolysis needle	Insertion into the follicle. Can use other sizes; I think the F part is important so that it fits the pen
TENS pad	Completing the circuit with the body
2mm pin connector	Connects to the TENS electrode
SSD1306 OLED display	For displaying the user interface. Not stocked on LCSC. Dual-colour is recommended
Foot switch	To turn the current supply on/off
3.5mm plug x2	For connecting foot pedal & electrode/needle to the board
Mini USB cable	Charging and programming
~5m ~24 gauge wire	Connecting the pen and TENS pad to the board
Lithium ion battery	Power
Single D-SUB female pin	Grips the electrolysis needle
Rubber feet	Keeps the case from sliding around (it's very light!)