# Reducing voltage for analog input, or how to reduce number of wires needed?

TL;DR: I need to reduce the number of wires my setup is using. What would be the best way? A Voltage Divider?

Background:
I'm working on a project to design gloves that produce a lightshow effect for a Scarlet Witch costume. Each glove contains 3 flex sensors, values read and used analog via analogRead, and 2 RGB LED strips that will flash different colors. Each strip has 2 LED's on it, in series. I am not using the green channel on it, so I have 2 strips each with essentially 2 red LED's in series and 2 blue LED's in series. It's actually from an adafruit RGB led strip: https://learn.adafruit.com/rgb-led-strips/ where I desoldered the last LED in the series of 3 and jumped the connections so it only used two. I didn't need the 3rd LED, and it reduced the power needed from 12v down to where it can use a 9v battery.

So as I'm calculating, each glove will need 9 wires going to it. One is +3.3v or +5v as it will be running off an Arduino Pro Mini, I have both 3.3v and 5v available.

1: +3.3v or 5v
2: Bend sensor 1
3: Bend sensor 2
4: Bend sensor 3
5: +9v for LEDs
6: PWM for Red on Strip 1
7: PWM for Blue on Strip 1
8: PWM for Red on Strip 2
9: PWM for Blue on Strip 2


simulate this circuit – Schematic created using CircuitLab

My problem:
Every set of wires I have access to without heat shrinking stuff is 2, 4, or 8 wires. All of the connectors I have that will allow the gloves to be easily detached are 8 wire pins as well.

My problem is I'm trying to remove one of the 9 wires. One way to do that would run the flex sensors with 9v, and reduce the voltage back at the arduino. Would a resistor based voltage divider work? It would only be powered while the gloves are on, which will be at worst a 10% duty cycle (show them off for 30 seconds, walk around for a few minutes, etc). But would that work where I need to read a variable value? (The more the fingers flex, the light brightness and and pulse speed changes).

Is there a better way to do it? Everything I've ever read about voltage dividers with resistors is "just don't do it".

Or given what I mentioned above about the circuit, can anyone think of an ingenious way to consolidate one of the wires? The gloves are tight, fingerless leather gloves. There is VERY LITTLE room in them, otherwise I'd put the arduino in the gloves themselves, but the MOSFET's (or even transistors if I went that way) take up entirely too much room. Hence the 'power pack'.

Worst case I can take the flex sensor off the wrist (that turns the gloves on when your wrist is pulled back/up, like how spider-man bends his wrist when shooting webs) and turn the gloves on/off with a finger movement, but I'd rather not have to both program that, as well as having the gloves turn on accidentally if a finger twitches :)

• Can you sketch the circuit? – Scott Seidman Aug 1 '16 at 11:15
• Huh? Way too much hand waving. I got lost and gave up halfway thru the first paragraph. – Olin Lathrop Aug 1 '16 at 11:17
• Don't you also need a GND connection? Now you're at 10 wires. Does that help? ADC scaling via a divider can and does work, but it introduces some additional concerns. Output impedance of transducer? Input impedance of ADC? Noise/error sources? – M D Aug 1 '16 at 11:20
• The grounds are the 3 return wires from the flex sensors, and the 4 returns from the LEDs. The other stuff is not a concern. Just need to read how much the flex sensor is bent, it's a simple resistance flex sensor. – InfernusDoleo Aug 1 '16 at 11:28
• Chances are you actually could put the circuitry on the back of the hand/finger and barely notice, but it would be harder to develop that way. You could easily fit a small regulator to power the sensor though. Resistive dividers aren't out of the question, but they will interact with the sensor by loading it, complicating the design and interpretation somehow, but not beyond what can be achieved with a little effort. – Chris Stratton Aug 1 '16 at 14:11

There are a few ways to do this.

1. The Flex Gauge is a variable resistor, and already requires a voltage divider setup to work. All you would do is change the resistor value around. At 9V for a under 5V value, the bottom resistor should be about slightly greater than the lower resistance of the flex gauge. If the flex gauge is 30kohm unbent and 70kohm fully bent, then it should be around 35 kohm. A voltage divider calculator and multimeter can be used to figure it out. This removes the 5V wire.

simulate this circuit – Schematic created using CircuitLab

1. Modify the leds for 5V power. Two red diodes in series (2.2 + 2.2) and a resistor for 0.6V at 20mA is fine on 5V. The Blue diodes will need to be changed to parallel connections. One resistor for each blue diode. This removes the 9V wire.

simulate this circuit

1. Most complicated, place the flex gauges in parallel. Each with an offset resistor, this would result in a different value that could be interpreted by the ADC. In my calculations, one will have much less range than the others, and some overlap, but as simple on/off type sensors, that's not much of a problem. This removes 2 wires.

simulate this circuit

1. Combine 1 or 2 with 3. 3 wires down.

As a suggestion, use a USB power bank (one that doesn't turn off by itself or you may need to add a pulse setting). Much better than a 9V battery, rechargeable and convenient.

Alternatively, go smd and bare bones. A bare microcontroller, smd sot-23 transistors or mosfets, 1206 or 0805 are all small but hand solderable, keeping everything on the hand except for power, which could be a single 2 wire cable.

As a side note, I've done this to a UV led strip, modifying it for 5V power from a usb power pack for a costume as well. Worked great.

Is this what you are looking for?

R2 and R3 form the voltage divider you mentioned. D1 keeps the signal voltage within 5V + 0.6V just in case something bad happens.

The actual resistor values have to be adjusted according to the range of your flex sensor.

p.s.: it is possible that you may omit R2 or make it very low, it just depends a lot on your flex sensor resistance range

simulate this circuit – Schematic created using CircuitLab