Rebuilding an old massage bed. Needing simple way to show roller height.

Thread Starter

randysgym

Joined Feb 2, 2021
4
This is my first post here. I am an novice in the world of electronic/electrical circuits, especially compared to those I've read here. I understand what resistors, relays, potentiometers, and leds are...basically. I'll do my best to research to figure out any help you can give me. So thanks in advance for any help you can offer.

Someone gave me an old chiropractic electric massage bed. The switch wiring had been badly hacked up (literally and figuratively). I've now got all 4 motors working properly (up&down, back&forth, rollers forward&backward, and vibration). It's quite heavily built, weighing in at around 250lbs (about 110kg).

The display panel is missing a way to show the height (up&down) level of the massage rollers. I was thinking to buy a slider potentiometer which would be mechanically controlled by the roller carriage rising and lowering. Then the voltage variations given by the potentiometer slider movement could be simply shown on a small volt meter mounted into the control panel.

The bed is powered by 120VAC on a 15amp circuit.

If I got a potentiometer and volt meter capable of handling that much power, would I need any other parts to make my simple circuit work reliably and safely? If so, what parts and some idea of how to wire it up, please?

Another question...
If I wanted to also wire in an LED to indicate power-on, would I need a special kind of LED, or just a resistor ahead of it? If yes on the resistor, what size?

If all this is not really electronic or somehow insulting to this forum please accept my apologies. Any help in directing my questions to a better source would be equally appreciated. Thanks for reading.
 

Sensacell

Joined Jun 19, 2012
2,819
That can work- does the unit have any DC power available inside?
Do you have a panel meter selected yet?

If you can rig the POT to move the full travel it's simple, a bit more complex if you need to offset and scale the range.
 

Thread Starter

randysgym

Joined Feb 2, 2021
4
That can work- does the unit have any DC power available inside?
Do you have a panel meter selected yet?

If you can rig the POT to move the full travel it's simple, a bit more complex if you need to offset and scale the range.
No DC power in the unit. It's all 120vac. I can position the pot to get the full range of the slider, no problem.

I haven't selected a panel meter yet. I was looking at an analog one that shows zero to 150 volts. Then I could open the face of it and insert a custom face showing "low" and "top" or something like that. Maybe 2 or 3 inches across.
 

Sensacell

Joined Jun 19, 2012
2,819
This circuit should do the job, the resistor that is in series with the meter needs to be chosen for the specific meter you decide on.
You can tweak the CAL pot to read full-scale at the end of travel.

The transistor buffers the voltage signal from the POT, the diode compensates for the Vbe drop on the transistor.

Note that variations in the power supply voltage will affect the reading, use a regulated supply.

meter.jpg
 

Thread Starter

randysgym

Joined Feb 2, 2021
4
Thanks so much for taking the time to help me. After some studying of your proposed circuit diagram, I have ordered the parts I need. Since I am doing this on a shoestring budget (haven't worked since last March), I made a few adjustments to your proposal to take advantage of some parts I had on-hand. I found a 9vdc power supply left over from an old land-line phone. Then I commandeered Christmas lights in place of LEDs. Much thanks again.

Randy in St Louis
 

JoshR77

Joined Feb 23, 2021
3
This is my first post here. I am an novice in the world of electronic/electrical circuits, especially compared to those I've read here. I understand what resistors, relays, potentiometers, and leds are...basically. I'll do my best to research to figure out any help you can give me. So thanks in advance for any help you can offer.

Someone gave me an old chiropractic electric massage bed. The switch wiring had been badly hacked up (literally and figuratively). I've now got all 4 motors working properly (up&down, back&forth, rollers forward&backward, and vibration). It's quite heavily built, weighing in at around 250lbs (about 110kg).

The display panel is missing a way to show the height (up&down) level of the massage rollers. I was thinking to buy a slider potentiometer which would be mechanically controlled by the roller carriage rising and lowering. Then the voltage variations given by the potentiometer slider movement could be simply shown on a small volt meter mounted into the control panel.
How is it now?
 

Thread Starter

randysgym

Joined Feb 2, 2021
4
How is it now?
Oh, I'm excited that y'all cared enough to ask. Thanks.

Just finished last weekend, actually. It works completely and beautifully. Best of all, getting to finally use the bed/table is massaging out all my aching back muscles from bending over doing all that work. ;-)

Thanks to all for the important assist.
 

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