using an analog potentiometer to activate digital inputs?

**scott_fx** · 07-30-2011, 12:23 PM

Hey guys,

so i have 4 mjsgadgets usb-io-1's and im using all of the outputs which gives me 16 unused digital inputs.

i have a hydrofoil that rotates 90 degrees and i'd like to have a better idea of where it is at any moment. I plan on hooking up a waterproof potentiometer or a hall effect ic that can detect rotation and give a linear analog output.

i could always get a phidget 1011 but was thinking about reducing the amount of parts and cost of the project by utilizing the digital inputs.

i was wondering how i would convert the 90 degree sweep into 16 digital switches. could i do it with a resistor ladder type setup? For instance. if the hydrofoil rotates from 0 degrees to 10 degrees the pot (which is attached to at the pivot point) would rotate and therefor increase the voltage from 0 to say 1v. then when it went to 20 degrees it would go up to 2v. how would i toggle a digital input when it hit 1v and then a second one when it hit 2v and so on?

**OldSpark** · 07-30-2011, 02:14 PM

It usually done with 16 point switches - whether optic, magnetic, mechanical.

But rather than an external analog to "digital" converter, you should be ale to use a voltage input and have your smarts decode into whatever output you want. Otherwise yes, an analog to 16 out (4 bit or higher) Analog to Digital converter. (Or Voltage to frequency & freq to one-of-16 outputs using an LM2917 & two 4017s; else voltage to digital output using LED drivers like the LM3914.)

**scott_fx** · 07-30-2011, 06:52 PM

i was anticipating your reply oldspark.

i dont know if the usbio1's can detect specific voltage. i'll email mitch and ask.

thanks, i'm looking into LM3914 right now

**scott_fx** · 07-30-2011, 06:57 PM

awesome suggestion.

quick search brought up this:
http://www.youtube.com/watch?v=O1X19...embedded#at=44

this is exactly what i would need.

http://engineeringshock.com/lm3914-b...ator-p-37.html

**OldSpark** · 07-31-2011, 12:13 AM

USB won't detect - I meant the analog input of whatever smarts you are using - eg, FusionBrain, Audrino etc.

In old days it was called an ammeter.
They used this silly mechanical "guage" called "moving vane"....
You'd connect your (say) 1mA (am)meter between the resistive position sensor and the voltage source (say 12V).
Its 90-degree arm would indicate the position (at whatever 1:1, 1:2 scale etc). For rudders, center- scale was straight ahead.
It uses only a single wire (plus return) despite its amazing bits or resolution (a superior encoding method to digital - at was called analog).

These days we have to cascade two LM3914s etc.

PS - some cars still use those meters - eg, fuel, temp.

**scott_fx** · 07-31-2011, 02:10 AM

Originally Posted by OldSpark

USB won't detect - I meant the analog input of whatever smarts you are using - eg, FusionBrain, Audrino etc.

In old days it was called an ammeter.
They used this silly mechanical "guage" called "moving vane"....
You'd connect your (say) 1mA (am)meter between the resistive position sensor and the voltage source (say 12V).
Its 90-degree arm would indicate the position (at whatever 1:1, 1:2 scale etc). For rudders, center- scale was straight ahead.
It uses only a single wire (plus return) despite its amazing bits or resolution (a superior encoding method to digital - at was called analog).

These days we have to cascade two LM3914s etc.

PS - some cars still use those meters - eg, fuel, temp.

oh yeah, i understood. the usbio1 is a the name of the i/o board/smarts im using.

**OldSpark** · 07-31-2011, 02:40 AM

I have no idea why you'd want to use usbio1's for this application.

**scott_fx** · 07-31-2011, 02:30 PM

Originally Posted by OldSpark

I have no idea why you'd want to use usbio1's for this application.

because i have 4 of them an none of the inputs are being used. that's why i wanted to get the analog to digital converter.

i'm up in the air if i just want the 16 points of resolution or if i want to get something with a true analog input

**OldSpark** · 07-31-2011, 09:04 PM

Ok, goodluck.

**scott_fx** · 08-02-2011, 06:21 PM

think im going to go full analog route instead. im just limiting myself with 10-16 steps. Im going to hold off until rrfusion works with the latest fusionbrain release. thanks oldspark