Hey guys, first time poster. I hope someone might be able to help.
My back ground is mainly in mechanical engineering and using basic arduino circuts for motion controls. I have never had to make a circuit, I mainly just purchase premade boards for their functionality.
Here is what I need to accomplish, but I am having a hard time finding the right information to fit my situation. I need to reference a 0-300 volt DC line voltage from a plasma cutter. Then I need to output a voltage between 0-12vdc max. peferably 0-5vdc.
Now one would assume a simple resistor voltage divider would do the trick, but I need some smoothing and isolation built in. Smoothing to remove spikes from the line voltage and isolation due to some high frequency pulses at start up.
Can anyone give me some direction to accomplish this? Obviously there is risk involved with high voltage, but I a comfterable with it with some caution.
Then I need to output a voltage between 0-12vdc max. peferably 0-5vdc.
For what purpose? Voltage dividers are for low current "signals", not for power. i.e. You couldn't make a proper cell phone charger with a voltage divider.
However, you could make a 300:5* voltage divider to measure the 300V with the Arduino. Or, you could run it into a digital input to measure on/off.
Smoothing to remove spikes from the line voltage and isolation due to some high frequency pulses at start up.
Is this going into an Arduino? If so, it would be a good idea to add a [u]protection circuit[/u] to protect from over-voltage or negative voltage. (The protection circuits require a resistor to limit current so you don't blow the diode(s) but your voltage divider will provide the resistance.)
You can make a low-pass [u]RC filter[/u] by putting a capacitor on the "output" of the voltage divider. The "R" is effectively the parallel** combination of both resistors, which is approximately equal to the lower resistance (when one resistance is much higher than the other).
For a quick-and-dirty approximation you can calculate the RC time constant. For example, multiply 1 meghom by 1uF which gives you a time-constant of 1 second, which is 1Hz. (The -3dB cutoff frequency is actually lower at 0.159Hz.)
If you wanted to measure 300V you'll need to calculate your resistors so you can read slightly-above 300V. Otherwise if you go over it will "max out" and you'll just read 300V.
** The resistors are in series, but the capacitor charges/discharges through both so the capacitor "sees" the resistors in parallel.
The output voltage is going to a torch height control. Basically if I want 150 volts, and the divider shows 130 volts it will move the Z height of the torch to match the desired voltage.
The out put is absolutely low current sensing. And yes, my intention is to use the arduino to smooth the input signal through programing unless I am able to do this with hardware.
Mainly I need the circuity to read the high voltage and protect the output from high frequency spikes. Perferably isolating it from the arduino out input of the CNC control.
Forgive me if my terminology is off, I am by no means more then a hobbyist.
This is not difficult and a voltage divider would do the job: If you use a resistor divider and an op amp as filter / voltage follower (to lower the impedance of the low voltage)
Then this voltage need to be isolated, for example with an analog optocoupler such as
I have never used this circuit but from the description it (or it's friends) should do the job
make sure your resistors a 'long enough' for the high voltage else use some in series and implement them as to respect the required distance for high voltage.
A schottky diode with anode at the OP AMP non-inverting input, and cathode at 5V, might not be a bad idea. Especially if the high voltage before strike is an issue. One, would need to work out the resistance values to ensure nothing fries.
Also, all you would need is an LM321 [the LM324 has four amps -- the LM321 has only one]. But, the fact that the LM321 only seems to be available with an SMD package, maybe not?
