The ancient Greeks and Romans harnessed steam for health and beauty much the same way we do today. Steaming your face might seem simple enough if you have running water, a way to heat it, a pot to keep it in, and a towel to drape over your head. Luckily, there are plenty of affordable at-home facial steaming products (usually called water steamers/vaporizers) on the market. If you opt to do it yourself way, then the potential benefits could be the cost and convenience. This is the photograph of a cheap steamer I bought from an online store a while ago. It is priced under $3.
Now you can use a home vaporizer as a quick gizmo for face steaming! When you are ready to start steaming, the first thing you need to look out for is the water/steam temperature. If you carelessly (and rapidly) get too close to the hot steam, you could blister your skin, which can leave behind a pock. Most beauticians recommend 110°C water/steam temperature and 30 to 45cm distance.
My cheap steamer/vaporizer is a simple AC230V water boiler and has nothing luxurious like a temperature level readout or timer control knob. Of course, we can get it fancier by adding funny blinkers and beepers, but in most cases, there is no need to. I simply built an add-on for my steamer which is a temperature bar graph display made with the help of a couple budget parts. In this post, you will learn how to replicate that compact temperature bar graph design idea to display the water/steam temperature level of your favorite facial steamer.
This is the schematic (v1) of the add-on temperature bar graph display. The entire circuit is powered at 5VDC (battery, dc external power supply adapter or usb power bank).
The key component in this schematic is the LM3914 dot/bar display driver (IC1). I chose this IC because it is an easily available monolithic integrated circuit that senses analog voltage levels and drives 10 LEDs providing a linear analog display. A single pin (Pin 9) changes the display from a moving dot to a bar graph. Current drive to the LEDs is regulated and programmable, obviating the need for extra resistors. Here, the setup forms a 1.2V FSD (full scale deflection) DC voltmeter.
Note that the low ends of the internal reference and divider are grounded, and their top ends are tied together, so the meter has a basic full sensitivity of 1.2V, when R0 = 0Ω.
↗ FSD = 1.25V ( 1 + R0/R2) , ILED = 12.5/R1
The 1K2 resistor (R1) wired across the internal resistance sets the on current (ILED) of all LEDs at about 10mA.
LM3914 Datasheet https://www.ti.com/lit/ds/symlink/lm3914.pdf
I used a 10-LED RYG (red-yellow-green) bar graph display because I wanted to make the final build nice and compact. The LED bar graph holds one red LED, two yellow LEDs and seven green LEDs. It is also easy to use discrete LEDs for each step but remember to use different color LEDs. The change in color gives an indication of how hot things are running.
LED Bar graph Datasheet Example https://components101.com/sites/default/files/component_datasheet/LED-Bar-Graph.pdf
The temperature sensor is a very popular precision centigrade temperature sensor chip LM35 (IC2). This precision temperature sensor IC, with an output voltage linearly proportional to the Centigrade temperature (Output = 0mV +/- 10.0mV/°C), operates from 4V to 30V, and has very low self-heating of less than 0.1°C in still air.
LM35 Datasheet https://www.ti.com/lit/ds/symlink/lm35.pdf
As pointed out, since the LM35 chip has a 10.0mV/°C output, it gives around 1.1V at 110°C and that’s close to the FSD of the LM3914’s current configuration. However, you can tweak the reading scale by using a suitable resistor/trimpot as R0.
Construction is non-critical, and it would be better to rig up on a small strip board, with the LM3914 and LED bar graph on the same circuit board, and the LM35 on flying leads suitably insulated with heat-shrink tube. A fairly important point is the location of the temperature sensor on the steamer. Here is one possible practical layout that I have planned:
A possibility that has not been tried yet is to use the highest temperature indication as a thermal cut out or limiter. This could be done by including an opto-coupler in series with the hottest LED (red) to operate an electromagnetic or solid-state relay as a steamer power supply cut out.
A compact and waterproof enclosure is essential to the completion of this project. You can pick any suitable prototype enclosure or soapbox. Alternatively, you can prepare your own enclosure using pieces of transparent acrylic sheet. You can find a simple front panel artwork suggestion below.
That is about it. Leave a comment below if you have any questions about this project. Also, feel free to share this idea if you know anyone that would find it helpful!
Addendum: To turn this into an electronic thermostat, all you need is a small relay driver circuit. You can use a transistor or an op-amp to do that. I would like to leave it as a homework for you. Anyway, an outline is shared below. Good luck with all your projects!