bend/flex sensor, regulated pulses

Thread Starter

d.z

Joined Oct 12, 2018
7
For a school project i'm going to build a virtual reality glove. to measure how much the fingers are bent i've built my own bend/flex sensors. the more i bend the sensors, the resistance becomes less (see the included picture and video for a test i did with the sensor). To make the glove comunicate with the computer i am using a Vive Tracker 2.0 . there are 6 pogo pins on the bottom of the tracker. one is ground, one is output and four are binary input pins. this means they can only measure a high and low voltage. this does not work for me, because i want to measure how much volt is going out of the sensor.

so i had an idea, what if you coud turn the amount of voltage into regulated pulses, and the more you bend the sensor the faster the pulses go. because the pulses are high voltage the Vive Tracker could be able to send the pulses to the computer. and with the game engine Unity i can measure how many pulses per second, and then bend the finger in the game.

so that's why i am creating this thread. i would like to know if there is a simple way to turn current into regulated pulses that go faster the more the sensor is bent.

AlbertHall

Joined Jun 4, 2014
11,695
This sounds like a classic application for the venerable '555.

Here R2 is your sensor and the supply voltage should match whatever the vive tracker needs.
What is the range of resistance of the sensor and what voltage does the tracker expect?

d.z
Thread Starter

d.z

Joined Oct 12, 2018
7

danadak

Joined Mar 10, 2018
4,057
If you are into embedded UPs thats fairly easy to do. Use
the A/D, measure the current, and translate that value into
period value for a PWM. Maybe < 20 lines C code.

Its a $4 board. And using chips other capabilities/resources add LCD, serial COM.........Note part has fairly accurate onboard Vref to make accurate measurements. You could also do this with 8 pin ATTINY UP and using basic language, Bascom AVR, do this as well. That part is <$1.

https://www.mcselec.com/index.php?option=com_content&task=category&sectionid=7&id=79&Itemid=57

Regards, Dana.

Last edited:
d.z
Thread Starter

d.z

Joined Oct 12, 2018
7
i made a bend sensor. with this i cant change the voltage output. the more i bend it the less resistance. i would like to turn the amount of volt coming out of the sensor into a signal with regulated pulses, and when i bend the sensor( so the resistance becomese smaller) the impulses become faster. i know that i can use a 555 timer chip. but i dont know how to wire the circuit. i want to use the circuit to give signals to my Vive tracker 2.0 . but the Vive tracker cant measure a difference in voltage so i am using pulses of high and low voltages because it can measure if the signal is high or low voltage.

i dont know the range of resistance of the sensor. and i think the supply voltage is 3.3 volt, i found it in the Vive tracker developer guide.

d.z.
Merged your new Thread with this existing Thread on the same Topic.
Mod:

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Thread Starter

d.z

Joined Oct 12, 2018
7
i'm trying to connect a sensor to 555 timer chip. i want to be able to change the frequency by changing the resistance with the sensor. how do i do this? the video i embedded is what i want to achieve at 3:13 . but i dont know how to wire the circuit.

also what would it look like if i wanted multiple sensors?

MOD Note: Please the same Thread for this Topic, Posts Merged.

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ericgibbs

Joined Jan 29, 2010
14,699
hi dz,
Do you have a 555 astable configured on your bread board , connected for audio .?
If so, post your circuit and we can suggest modifications.
Do you have the flex sensor on the bench.?
E

d.z
Thread Starter

d.z

Joined Oct 12, 2018
7
i dont have the 555 timer chip yet. but i've drawn a diagram. I put an "x" for the resistance of the reistors and the capacitors. how would the signal change if i increase the resistanc these of the resistors? i would like to get an as low frequency as posible. also i connected the output pin to the vive tracker pogo pin. and the ground to the ground of the vive tracker. but i dont know where to connect the + and - in the diagram. or do i just put a different battery in there? because i read that the chip needs a minimal of 5 volts, and in the vive tracker developer guide i found that the vive tracker outputs 3.3 volts.

ericgibbs

Joined Jan 29, 2010
14,699
hi Dirk,
What voltage level and frequency range do want on the pogo pin output.
Have you measured the resistance change, using an ohm meter, for the flexi sensor, min/max resistnace values are required.
E

Thread Starter

d.z

Joined Oct 12, 2018
7
i would like to have the pogo pin output a low frequency. probably between 1 and 20 hz. i have not yet measured the resistance change for the flex sensor. but i have done a test in wich i hooked the sensor up to a power supply and a resistance and then measured it with a computer. i'll add a image of the results. but i dont know if this is what you mean.

also if i where to make the circuit that i drew in a previous post and instead of connecting it to the Vive tracker i would connect it to a speaker. would the circuit work? because i copied the circuit from the video that i included a few posts ago.

D

ericgibbs

Joined Jan 29, 2010
14,699
hi D,
As you know the frequency of the 555 output is set by the resistance and cap values, so for 1 to 20Hz, we would need to the total resistance change of the flexi.
E

Thread Starter

d.z

Joined Oct 12, 2018
7
hey E,

then how would i get a low frequency on the output?

D

ericgibbs

Joined Jan 29, 2010
14,699
hey E,
then how would i get a low frequency on the output?
D
Let me know the total resistance change and we can then calc the values.

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