Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: lakepir8 on February 12, 2011, 09:37:07 AM

Title: SoR_Scope help
Post by: lakepir8 on February 12, 2011, 09:37:07 AM

I purchased the Axon controller specifically to use as a scope, and I want to look at 120v AC. Does it have to be modified?

What kind of probe do I need?

Title: Re: SoR_Scope help
Post by: hopslink on February 12, 2011, 05:53:51 PM

The SoR scope page (http://www.societyofrobots.com/sor_scope.shtml) says "By default hardware you can only measure 0V to 5V signals."

120V(rms) AC signal is -170V to 170V, so yes you need to do need to modify it. If you don't know how already then you really shouldn't be working with these sorts of voltages. My advice is to get someone who knows what they are doing to supervise you directly. All the best, and stay safe!

 

Title: Re: SoR_Scope help
Post by: lakepir8 on February 13, 2011, 07:21:58 AM

That's really not help. Is it even possible to use the Axon to measure 120V?

Title: Re: SoR_Scope help
Post by: waltr on February 13, 2011, 09:21:11 AM

It is possible BUT you need a properly designed circuit to:
1- reduce and shift the voltage to levels acceptable to the Axon, 0 to 5V.
2- provide adequate isolation to prevent electrocution.

What measurement of the AC Mains do you what:
VAC RMS
V peak
V Peak to Peak

Do more googling for circuits. A circuit that works for any 5V micro-controller will work. It doesn't need to be just for an Axon.
Some that I found:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1255308778 (http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1255308778)
http://www.microchip.com/forums/m138162-print.aspx (http://www.microchip.com/forums/m138162-print.aspx)
http://www.eevblog.com/forum/index.php?topic=106.0 (http://www.eevblog.com/forum/index.php?topic=106.0)
http://bbs.circuitcellar.com/phpbb/viewtopic.php?f=11&t=3612 (http://bbs.circuitcellar.com/phpbb/viewtopic.php?f=11&t=3612)

If you are just interested in look at the AC waveform then a 120 to 6.3V transformer and a resistor voltage divider is an inexpensive method that does provide isolation.

Title: Re: SoR_Scope help
Post by: Admin on February 13, 2011, 06:23:44 PM

lakepir8, you can buy sensors that will connect to the Axon ADC to let you measure 120 VAC.

For example:
http://www.cy-sensors.com/VoltageSensor.htm (http://www.cy-sensors.com/VoltageSensor.htm)
http://www.phidgets.com/products.php?category=8 (http://www.phidgets.com/products.php?category=8)

Are you trying to measure voltage or current?