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Possible Shield Requirements Analysis
05-31-2014, 12:44 AM (This post was last modified: 05-31-2014 12:45 AM by jmccartney.)
Post: #29
RE: Possible Shield Requirements Analysis
(05-30-2014 10:11 PM)steamboat Wrote:  All I need is an amplifier which can bring this some mV to a detectable voltage - don't know what to choose here in modern times ;.)

I think something like this would do what we want

I got the idea from this thread:
Where a user describes it use as:
Use a .1 ohm 1% resistor (or .05 1% if I can find it for a reasonable price in a 0805) between servo supply (+6V) and servo. I'll then have a MAX4372F connected across that resistor. Datasheet here: specifically I'd use a MAX4372FEUK-T (SOT-23) (or MAX4372HEUK-T if .05 ohm resistor). I'd then feed the AVR's AREF with a precision 5V signal. The MAX4372F multiplies the voltage across the resistor by 50, so that would give the ADC a range of 0-1A, which should be way more than enough. I'm going to run some tests to see if I can get current over half an amp - and if I can't I'll probabaly go with the MAX4372H (multiplies voltage by 100). Oh, I should mention that with a .1 ohm resistor I'll see a 1V/20 drop across the resistor, which I feel is small enough not to be worried about.

I would have to order the parts and actually try it out before I felt comfortable putting it on the PCB..(current sense is out of my element a bit).. Also we would not want to have more than one or two individual servos with this because of: routing issues, cost (1.50us) per chip, use of an analog line, space constraints. Maybe two servos would have current sense, and then have current sense on the entire PWR bus so we know the total draw of all servos/motors.. IDK. There might be a lower cost newer solution, this thread was 2005 i think, so i will have to look through more parts..
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Messages In This Thread
Power Management - steamboat - 05-13-2014, 05:34 PM
Servo current - steamboat - 05-30-2014, 10:11 PM
RE: Possible Shield Requirements Analysis - jmccartney - 05-31-2014 12:44 AM
Emoro - steamboat - 06-08-2014, 07:23 AM

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