Hello. Tried searching a bit but didn't see any topics posted related to what I'm doing.
My end goal is simple: I need to data log some analog voltage that varies over time.
Now to accomplish this, I've come up with a few ways. Please provide other cheap suggestions I haven't thought of. I've looked into building my own usb-like device (no computer I have has a serial port! lol). Programming the microcontroller, while I can accomplish it, it's a bit out of scope for my overall goal (graphing a few dozen tests for a bigger project).
Most likely I'd like to pick up one of these pre-built units instead:
http://numato.com/8-channel-usb-gpio-module
It's nice and inexpensive. Since it is basically a serial-over-USB, that means the fastest i can read is limited to the USB bus - about 10ms. The manual indicates that the device itself is a bit slow though, and could take about 50 to 100ms. For my purposes, that is fine (10 Per Second). I just need to read voltage and data log it over a long period of time.
The second purpose of this thread is to ask how to safely read these voltages with such a device. The device I am reading has variable voltages that range from 0 - 12 VDC and draws roughly 4 Amps of current (+/- 0.5Amp depending on temps). The USB serial device I linked to above has a max input of 5VDC, and obviously operates on a much lower current overall.
I don't want to blow it up. So obviously I need to scale this down. My resistor calculations are a bit rusty, so I ask everyone to verify my logic to do this safely:
1) take the input by connect jumper wires in parallel to the main load circuit.
2) solving for Vout = Vin * R1(R1 + R2) , I come up with two resistors: R1= 1kΩ and and R2 = 500Ω, respectfully.
3) install the R1 1kΩ 1/4 Watt resistor inline with the jumper wires from the positive+ side.
4) Then, install the R2 500Ω 1/4 Watt resistor in series connected to R1, and the other side of R2 connected to ground-.
5) I would then, finally, take a 3rd jumper wire at the R1 and R2 junction, to get 4V output from 12V on the main circuit.
I would like accurate readings, so is 1000 Ω and 500 Ω a good start? Should I go higher or lower?
Using small 1/4 Watt resistors is ok? Or because of the original 4 Amp load of the original circuit I am measuring, do I need some massive 5 Watt resistors instead?
Thanks in advance!
My end goal is simple: I need to data log some analog voltage that varies over time.
Now to accomplish this, I've come up with a few ways. Please provide other cheap suggestions I haven't thought of. I've looked into building my own usb-like device (no computer I have has a serial port! lol). Programming the microcontroller, while I can accomplish it, it's a bit out of scope for my overall goal (graphing a few dozen tests for a bigger project).
Most likely I'd like to pick up one of these pre-built units instead:
http://numato.com/8-channel-usb-gpio-module
It's nice and inexpensive. Since it is basically a serial-over-USB, that means the fastest i can read is limited to the USB bus - about 10ms. The manual indicates that the device itself is a bit slow though, and could take about 50 to 100ms. For my purposes, that is fine (10 Per Second). I just need to read voltage and data log it over a long period of time.
The second purpose of this thread is to ask how to safely read these voltages with such a device. The device I am reading has variable voltages that range from 0 - 12 VDC and draws roughly 4 Amps of current (+/- 0.5Amp depending on temps). The USB serial device I linked to above has a max input of 5VDC, and obviously operates on a much lower current overall.
I don't want to blow it up. So obviously I need to scale this down. My resistor calculations are a bit rusty, so I ask everyone to verify my logic to do this safely:
1) take the input by connect jumper wires in parallel to the main load circuit.
2) solving for Vout = Vin * R1(R1 + R2) , I come up with two resistors: R1= 1kΩ and and R2 = 500Ω, respectfully.
3) install the R1 1kΩ 1/4 Watt resistor inline with the jumper wires from the positive+ side.
4) Then, install the R2 500Ω 1/4 Watt resistor in series connected to R1, and the other side of R2 connected to ground-.
5) I would then, finally, take a 3rd jumper wire at the R1 and R2 junction, to get 4V output from 12V on the main circuit.
I would like accurate readings, so is 1000 Ω and 500 Ω a good start? Should I go higher or lower?
Using small 1/4 Watt resistors is ok? Or because of the original 4 Amp load of the original circuit I am measuring, do I need some massive 5 Watt resistors instead?
Thanks in advance!