Hi there, I’m kinda new to this (just got my ssc 20 minutes ago) and would like to know some basics about the I/O pins ABCD 
What I want to make is a battery level indicator with 2 zenner diodes.
But I dont really understand how the ABCD inputs work … can I apply voltage to them ? (without frying my ssc?:D)
Say for example apply the + from a 1.2V battery to A and the - from the battery to ground, will this display something like “62” if an VA command is issued ?
Thanks!
Sounds about right. Just don’t put more han 5v across the input pin. The board comes with two of the input pins jumpered to the board +5v and two jumpered to ground.
Hi
I want to see the voltage in a 12V battery using the analog inputs on my SSC-32. I know it will only go up to 5V and then I am assuming it will start to do funny things.
My theory is to put a 3 Ohm resistor in line with the VA terminal so that the voltage flows from the 12V battery into the resistor and then into the SSC-32 and of course back to a common ground. I am assuming the resistance in the VA is almost 100% so in this theory the resistor cuts the voltage from the 12V battery to a third. I will then multiply my VA values by 3 to get he voltage of the 12V battery in my program.
Will this work?
Thanks,
Um, no. And neither will the SSC-32 if you try the proposed circuit.
Think about this for a second. If the maximum allowed input voltage on VA is 5V and you have a 3 ohm resistor between your 12V battery and VA then you would need to drop 7V across 3 ohms… my ohm’s law foo puts I = V/R = 2.3 amperes… where do you think the SSC-32 VA input is going to put 2.3A?
Here is a test that will help lead you down the right path. Take a flashlight battery, say an AA sized 1.5V cell, and measure the voltage across it and write it down. Now connect the - side of the cell to ground, put your meter in mA current mode, wire the meter between the cell + and the VA input of the SSC-32 (with the SSC-32 already powered of course.) Record the current. Now use your ohm’s law foo to determine the approximate input resistance of the VA input to the SSC-32.
Let us know what you find and we’ll take the next step.
ohh yeah forgot about current. Duh. STOOPID.
Man I cant believe I actually passed physics 12 and then forgot about current.
I will try that tomorrow.
Thanks,
You may want to make a voltage divider to drop the 12v down to 5v. If you plug 47000 in for R1 and 33000 for R2, and 12v for the initial voltage int he below calculator, the result is ~5v. Add a 5.1v zener diode on the output for voltage spike protection and you should be good to go. The 47k resistor, the 33k resistor, and the zener diode are available at Radio Shack. As the 12v decreases, the divider output voltage also decreases.
This does not take the input impedance of the VA input into consideration, which would be in parallel with your 33K resistor. This is the reason I suggested the exercise above, to measure the input impedance, so it can be used to calculate the top resistor.
Also needing consideration is his “12V” battery might be anything from 11.6V to almost 15V when fully charged, depending on the type of battery. You can clip the higher voltages of course but it’s just as easy to consider them and choose resistors accordingly.
The 5.1V zener isn’t a bad idea but as you approach the 5.1V knee voltage it will start to leak more current and if the top resistor is large enough will introduce a non-linearity in the measurement. A 5.0V TVS (transient voltage suppressor) might be a better idea… basically it’s a specialty type of zener diode with a sharp cutoff knee and able to handle large energy surges like those associated with dynamic breaking a motor or even ESD hits.
What is missing is a small capacitor across the VA input to filter out motor switching noise and make the VA reading less erratic. What value capacitor to use could depend a bit on the voltage divider resistor values chosen.
My tinkering with the ssc-32 input pins in the analog mode indicates the impedance is probably very high. In the digital mode there is resistor in the circuit (per the ssc-32 manual), but in the analog mode the pins actually float.
I got a 47k and 33k resistor from Radio Shack and put them in series as a voltage divider. With a ~12.5v wallwart voltage source, the center output was ~5.1v. I put a 5.1v zener diode in as a potential protection device, but that dropped the output down to ~3.5v. I’ve read that zeners need several ma of current to function properly, which would not be available thru the 47k resistor in this divider.
