I will use PWM to control the speed of the Motor. If I put the sensing resistor in series with it and feed the resistor's voltage drop to the ADC, then the input to the ADC will be a square wave! (has the frequency and duty cycle of the PWM) which is bad. I think I will need some circuit to average it out... Thomas >From: "Eisermann, Phil [Ridg/CO]" >Reply-To: pic microcontroller discussion list >To: PICLIST@MITVMA.MIT.EDU >Subject: Re: [OT]:Current Sensor >Date: Thu, 5 Apr 2001 13:04:44 -0500 > > The resistor *is* your current to voltage converter. Not sure how >you're controlling the motor (PWM? FET/BJT? simple on/off?), but if one >side >of the resistor is tied to ground, you can use an op-amp (non-inverting >configuration) to scale the small voltage drop across the resistor into >0-5V >for A/D conversion. Beware, though. The motor current will have a lot of >noise. Some low-pass filtering before the A/D wouldn't hurt. > > I like the SenseFET for this application. International Rectifier >IRCZ44 comes to mind, although you might not get much accuracy because >that's a 50A device. It's a 5 pin MOSFET. The extra two pins are an >integrated 'current tap' This current tap reflects a fraction of the >drain-source current. You convert this scaled down current with a resistor. >The advantage is that you don't have the current-sensing resistor wasting >power. You only have the on-state resistance of the FET to worry about. For >the IRZC44, that's 0.028 Ohm. Only drawback is that since the motor is 2.5A >and the FET is 50A, you might not get much accuracy because the load is >such >a small fraction. You'd need a large gain on the op-amp, and possibly >correlate some actual current readings with output to get good results. Or >you could use a different version of this FET (one with less range). >DigiKey >now carries these types of FET's, so you might start there to see what you >can easily get. > > >-----Original Message----- >From: Thomas N [mailto:thomasn101@HOTMAIL.COM] >Sent: Thursday, April 05, 2001 12:28 PM >To: PICLIST@MITVMA.MIT.EDU >Subject: Re: [OT]:Current Sensor > > >Do you know the part number for the current to Voltage converter IC? >THomas > > > >From: Vasile Surducan > > > >Use a small resistor and a curent to voltage converter. > >example: 0.1 ohm , 25mV to 250mV drop-out, > >convert this potential with a good operational amplifier to 0-5V > >Vasile > > > >-- >http://www.piclist.com#nomail Going offline? Don't AutoReply us! >email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body