Hello everyone! I’m currently working on a project that has 3 analog inputs that I need to convert to digital signals to be passed through microUSB to smartphone software.
I’ve been looking around and I’m not quite sure if this (https://www.adafruit.com/products/1501) would be a viable option or if there is a better option out there, mind you I’m no electrical engineer and most of what I know I’ve learned messing around on sparkfun.
My goal is to keep the project as inexpensive and small as possible.
Anyhow, any help is greatly appreciated and thanks in advance.
I’m a complete amateur at this, but I’ll give it my best.
The USB will need to power the phone (5Volts) while feeding the phone via microUSB digital signals from 3 analog inputs:
a temperature gauge
an RPM cable reading straight from a coil
a magnetic based speedometer
The digital signals will then be processed by a smart phone application. I imagine there will be no resolution? Measurements will be taken fairly often as the RPMs have to be calculated. I do not believe any filtering will be needed. As far as the fuse, I imagine just one fuse from the hardwired battery supply to the board.
The signal from the coil will probably have to be level-shifted and have the edges sharpened up.
What temperature ranges do you need to measure?
Magnetic-based speedometer means what?
To answer you question, the Trinket will probably work for your application. If not the Sparkfun ProMicro has plenty of I/O. However, the choice of processor board is probably the most minor thing to think about.
Start by figuring out exactly what your sensors output. That will tell you how to process them. You may be able to find this out from the data sheets or service manual, or you may need to grab a scope and look.
Temperature probably is a voltage (it could also be a digital signal). It will likely need some conditioning since it is doubtful that it is in the right range for your ADC - at least a divider
RPM - this needs to be cleaned up before feeding your micro as it will likely have nasty spikes on it due to the coil. Once cleaned, it is probably best to treat this as a digital signal since you need to either count pulses or measure time between pulses.
Magnetic speedometer - is there some electrical signal coming from this? Again, this could be digital or analog
All of these connect to things in the real world, and worse to signals in a vehicle. That’s a very electrically hostile environment. You will need voltage and current limiting, filtering, zener clamps, MOVs, fuses and other similar protection to keep from blowing up the inputs on your micro or providing noisy signals for measurements. If you are powering it from an auto’s electrical system, that will also need more than just a fuse. Read up on “load dump”…
Resolution on an ADC is how many bits it has - what is the smallest change in voltage it can descern.
I’m not clear on the difference between these two. Sounds like they are two of the same kind.
These are most likely the same kind, the coil will send an electrical pulse down the cable straight to the converter to be calculated same with the speedometer. Every time the magnet on the wheel rotates it sends a pulse to be calculated as well. The thermometer will merely measure voltage.
You need to find out more information before you can proceed…
The thermometer will merely measure voltage
.
What is the range? Is it 0-1V, millivolts from a thermocouple, 0-5V? What is the range you will get for the temperatures you are planning to measure? Is it linear? What resolution do you need to measure (to the nearest tenth of a degree, degree, nearest 100 degrees?)
the coil will send an electrical pulse down the cable
As mentioned above - what voltage? What pulse width? How much noise? Analog or digital?
The answers for these will tell you what you need to do to these signals before your micro can handle them.