Author Topic: How to build a current sensor?  (Read 1178 times)

0 Members and 1 Guest are viewing this topic.

Offline random robotsTopic starter

  • Full Member
  • ***
  • Posts: 108
  • Helpful? 3
  • he drives worse than my robot... thats sad
How to build a current sensor?
« on: July 10, 2010, 01:59:31 PM »
Can you post shematics if possible? I would like the sensor to detect if the current to the motor is less than 3A.

Thanks,
Patrick
« Last Edit: July 10, 2010, 03:25:36 PM by random robots »
this is a signature.

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: How to build a current sensor?
« Reply #1 on: July 10, 2010, 02:47:10 PM »
Hi,

If you can afford to drop 0.7V, a resistor of 0R47 in series with the positive supply and a PNP transistor with the emitter to the supply side of the resistor, the basis on the other side and a pull down resistor from the collector to ground.
The collector will go positive with a current draw of more than ~1.5A and low otherwise.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline random robotsTopic starter

  • Full Member
  • ***
  • Posts: 108
  • Helpful? 3
  • he drives worse than my robot... thats sad
Re: How to build a current sensor?
« Reply #2 on: July 10, 2010, 02:55:05 PM »
okay, this is what I got from this.

resistor>PNP>pull down resistor>ground
current-/

Am I correct?
Also what does the pull down resistor do in the circuit?

Patrick
edit: no, i do not want to have a voltage drop at all if possible. thanks for the help though.
« Last Edit: July 10, 2010, 03:13:06 PM by random robots »
this is a signature.

Offline Choco_liger

  • Full Member
  • ***
  • Posts: 81
  • Helpful? 3
Re: How to build a current sensor?
« Reply #3 on: July 11, 2010, 03:29:32 AM »
If your worried about it damaging it, you could use a 3amp fuse.

Won't really measure it, but it can tell you if it's higher than 3amps.

Offline dunk

  • Expert Roboticist
  • Supreme Robot
  • *****
  • Posts: 1,086
  • Helpful? 21
Re: How to build a current sensor?
« Reply #4 on: July 11, 2010, 04:32:44 AM »
If you can afford to drop 0.7V, a resistor of 0R47 in series with the positive supply and a PNP transistor with the emitter to the supply side of the resistor, the basis on the other side and a pull down resistor from the collector to ground.
The collector will go positive with a current draw of more than ~1.5A and low otherwise.

there are transistors designed for a purpose similar to Soeren is describing.
i use http://www.zetex.com/3.0/pdf/zxct1009.pdf .

it differs from a simple transistor in that instead of a simple high/low output,
the ZXCT1009 will give you an analogue output voltage proportional to the input current.

whether you choose to use the ZXCT1009 or not, it's datasheet will clarify the layout Soeren described.


dunk.

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: How to build a current sensor?
« Reply #5 on: July 11, 2010, 06:29:58 AM »
Hi,

edit: no, i do not want to have a voltage drop at all if possible. thanks for the help though.

OK, This device is the closest to zero drop that you get.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline random robotsTopic starter

  • Full Member
  • ***
  • Posts: 108
  • Helpful? 3
  • he drives worse than my robot... thats sad
Re: How to build a current sensor?
« Reply #6 on: July 11, 2010, 06:50:05 AM »
dunk, your link appears to be broken
this is a signature.

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: How to build a current sensor?
« Reply #7 on: July 11, 2010, 06:52:23 AM »
Link appears fine, but I get a zero length file.

This works (darned, Zetex was sold :()
http://www.diodes.com/datasheets/ZXCT1009.pdf

« Last Edit: July 11, 2010, 07:00:09 AM by Soeren »
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline random robotsTopic starter

  • Full Member
  • ***
  • Posts: 108
  • Helpful? 3
  • he drives worse than my robot... thats sad
Re: How to build a current sensor?
« Reply #8 on: July 11, 2010, 06:57:46 AM »
i can only get to the cached file.
this is a signature.

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline random robotsTopic starter

  • Full Member
  • ***
  • Posts: 108
  • Helpful? 3
  • he drives worse than my robot... thats sad
Re: How to build a current sensor?
« Reply #10 on: July 11, 2010, 07:11:11 AM »
thanks. new question- how do i connect the motor to the current sensor. does it go from v sense- to ground, or does it connect to the Iout as well?

Thanks,
Patrick
this is a signature.

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: How to build a current sensor?
« Reply #11 on: July 11, 2010, 09:16:16 AM »
The datasheet shows!
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline random robotsTopic starter

  • Full Member
  • ***
  • Posts: 108
  • Helpful? 3
  • he drives worse than my robot... thats sad
Re: How to build a current sensor?
« Reply #12 on: July 11, 2010, 02:37:11 PM »
what do i use vout for? Scratch that. I think i got it.

Patrick
« Last Edit: July 11, 2010, 02:46:40 PM by random robots »
this is a signature.

 


Get Your Ad Here

data_list