Isolation

[lerameur]

Hello,

I am building a robot and wanted to have isaltion between the
microcontroller and the motor. So Iknow have two batteries (one for
each) . I aslo want to have a voltage checker for each battery.
Because the reference value is not present when I calculate the
voltage on the motor battery I am not able to determine the voltage.
I am using a A/D conversion, but seen from the microcontroller , the
motor battery is floating. (no good)
I thought of using an opto coupler but some advise me not to because
they are non linear. I looked for some isolation amplifier, but these
chip are very expensive. Any alternative I could use that could give
me a fair reading ?

thanks

ken

 

[Noway2]

Hello,

I am building a robot and wanted to have isaltion between the
microcontroller and the motor. So Iknow have two batteries (one for
each) . I aslo want to have a voltage checker for each battery.
Because the reference value is not present when I calculate the
voltage on the motor battery I am not able to determine the voltage.
I am using a A/D conversion, but seen from the microcontroller , the
motor battery is floating. (no good)
I thought of using an opto coupler but some advise me not to because
they are non linear. I looked for some isolation amplifier, but these
chip are very expensive. Any alternative I could use that could give
me a fair reading ?

thanks

ken

Take a look at instrumentation and difference amplifiers. Analog
Devices has a pretty good website. I believe that both types of amps
can give you a pretty high degree of isolation when used properly. This
is especially true of the instrumentation amps, but I also think that
they are usually designed with a high gain, so they may or may not work
for your application.

 

[default]

Hello,

I am building a robot and wanted to have isaltion between the
microcontroller and the motor. So Iknow have two batteries (one for
each) . I aslo want to have a voltage checker for each battery.
Because the reference value is not present when I calculate the
voltage on the motor battery I am not able to determine the voltage.
I am using a A/D conversion, but seen from the microcontroller , the
motor battery is floating. (no good)
I thought of using an opto coupler but some advise me not to because
they are non linear. I looked for some isolation amplifier, but these
chip are very expensive. Any alternative I could use that could give
me a fair reading ?

thanks

ken

You could still use a simple optical coupler - just calibrate against
a lookup table in memory.

If the two batteries can share a common ground there's no problem.

If they have to be separated - ask yourself why you need isolation?

Just to keep the motor supply from talking to the data supply? If
that's the case you can use a high impedance op amp (something like a
Jfet input amp) and use relatively high series resistance into the
differential inputs - it won't be "isolated" strictly speaking, but no
significant current will be exchanged by the two systems, and no
noise.

A cheap and dirty isolation trick is to use something like a two pole
double throw relay and charge a cap with the motor voltage then switch
the relay and read the voltage on the cap.

Another technique is to use a voltage to frequency converter on the
motor side to send a string of pulses over to an optical coupler whose
frequency is proportional to the motor voltage. You read the
frequency at the micro controller and calculate the voltage or convert
the pulse train back to a voltage level with a frequency to voltage
converter.

 

[John Fields]

Hello,

I am building a robot and wanted to have isaltion between the
microcontroller and the motor. So Iknow have two batteries (one for
each) . I aslo want to have a voltage checker for each battery.
Because the reference value is not present when I calculate the
voltage on the motor battery I am not able to determine the voltage.
I am using a A/D conversion, but seen from the microcontroller , the
motor battery is floating. (no good)
I thought of using an opto coupler but some advise me not to because
they are non linear. I looked for some isolation amplifier, but these
chip are very expensive. Any alternative I could use that could give
me a fair reading ?

Flying capacitor input to the ADC: (View in Courier)


+----------->\ <--------[ADC]--->DATA
| \ |
| O |
| | |
[MOTOR BATTERY] [CAPACITOR] |
| | |
| O |
| / |
+----------->/ <----------+----GND