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1  Using Arduino / Sensors / Re: Sensor suggestions for measuring DC amps, from +100A to -10A on: March 19, 2012, 05:12:30 pm
Stainless steel has higher resistance than Copper or Aluminum so at higher currents it starts to heat up. Its only a problem if high current passes through stainless steel, like washers or nuts in between the wire lug and the sensor pads(Ive seen this too often), but if its just used to fasten the lugs directly to the sensor pads then thats aok.

If you need to place washers and nuts in between the sensor pads and wire lug(to prevent squishing the PCB) then use nickel plated copper. Dont forget lock washers or loctite, you dont want loose nuts at those currents.

Thanks

Roy
2  Using Arduino / Sensors / Re: Sensor suggestions for measuring DC amps, from +100A to -10A on: March 19, 2012, 11:08:16 am
Ninja,

I would like to chime in on the current capacity since most of your questions were answered by MarkT and dc42.

The 100A physically can handle 125 amps (more in brief moments). Ive tested it constantly at 110Amps. The only issue I see is that linearity seems to suffer after 100amps also heat build up will change the devices' sensitivity. So make sure your connection to the sensor can handle the current(no stainless steel hardware please) otherwise heat would be an issue.

Roy
3  Using Arduino / Project Guidance / Re: Please Help me find the best solution for my important project! on: February 14, 2012, 03:35:57 pm
We were testing something similar when I was in Asia. We basically created a wireless network using Ubiquiti equipment, then used the Ethernet shield to get the arduinos online at different points(the sensors where monitoring pumping stations with about 1km distance from the control center). We did not get to test the system as much as we wanted because it was scrapped early on but it did worked. The Arduino part is the least of your problems, getting a city wide wireless network needs an RF guy to things off the ground.We grouped nearby installations and used a backhaul to send data to the central location, 2.4ghz for the points and 5ghz for the backhaul. A local guy is handling the arduino setup, we were there for the wireless side.

Techone is right, get a couple of wireless equipment and test it at home, this is how we started. Just make sure to turn down power as it can overwhelm nearby equipment and also be mindful of your country's RF power limits. 
4  Using Arduino / General Electronics / Re: 8-14V input with regulated 12V output needed on: February 13, 2012, 02:20:45 pm
You would need a sepic or buck/boost switching power supply. Search for them on ebay. They have modules that can power up to 2 Amps.
5  Forum 2005-2010 (read only) / Syntax & Programs / Re: Stop after # of loops on: May 07, 2007, 12:04:13 pm
Thanks jims it worked!!  smiley-wink

Roy
6  Forum 2005-2010 (read only) / Syntax & Programs / Stop after # of loops on: May 06, 2007, 06:04:55 pm
Hi,

I modified the LED BLINK code to run 2 solenoids(followed the tutorial on solenoids) and was wondering how do I stop after a specified number of loops say 20,000 actuations? I was also thinking of using a selector with resistors so I can select the number of loops before it stops, say 10K, 20K and 30K, but thats still way ahead of me as Im a real newbie with this stuff. Just stopping the loop will be ok for me now.

Using the USB version.

Thanks

Roy
7  Forum 2005-2010 (read only) / Development / Re: Introducing the MEGA_Stick on: August 21, 2010, 11:22:09 pm
Nice!

I hope you have a large pad under the 7805, they get toasty at automotive voltages even at 1/3 of an amp.
8  Forum 2005-2010 (read only) / Development / Barebones with SMT Chip schematics on: June 12, 2010, 02:28:00 am
Hi,

Do you guys know of any Arduino variant similar to this.

http://www.moderndevice.com/products/rbbb-kit
or this
http://wiblocks.luciani.org/PICO/PICO1TR-index.html

that has an SMT chip?

Or maybe someone can show me how to do away with the USB chip on the Stickduino or the Seeeduino schematics.

http://spiffie.org/kits/stickduino/start.shtml
http://www.seeedstudio.com/depot/seeeduino-v328-fully-assembledatmega-328-p-439.html

Thanks
9  Forum 2005-2010 (read only) / Interfacing / Re: 48 V signal though opto isolator into Arduino on: October 08, 2010, 01:07:42 pm
stealthtransam,

What kind of linearity are you getting with the optocoupler? I was thinking of going with the LOC110 which is supposed to be linear but I haven't received it yet. The regular opto couplers suffers from non-linear outputs thus not recommended for ADCs.

The problem I have is being able to measure -48 v systems and +24v systems with one unit. Altho I found a solution for that(relays, voltage inverter), I am still looking for alternate solutions.
10  Forum 2005-2010 (read only) / Interfacing / Re: Isolate ADC inputs on: September 21, 2010, 10:50:52 am
Thanks Richard for all the info. I'll try that relay trick. I'll get a new PCB done from dorkbotpdx.
11  Forum 2005-2010 (read only) / Interfacing / Re: Isolate ADC inputs on: September 20, 2010, 08:40:12 pm
Richard,

How would I wire the relay? If one ADC input measures +GND and -48 and the other input measures +12 and GND, this would short -48 to GND.

Thanks

Roy
12  Forum 2005-2010 (read only) / Interfacing / Re: Isolate ADC inputs on: September 20, 2010, 07:45:17 pm
Richard,

I am making the meter, its an arduino with LCD. It monitors current, voltages, battery temp and a low voltage disconnect. Yes, these are pretty major stuff but the meters are only for monitoring. I think the problem is with the ADC measuring multiple voltages at different GND levels. So its more of a data acquisition type of equipment than a  regular digital meter. If it only measures 1 voltage then an isolated power supply will work just fine.

retrolefty,

Thats what Im using on the supply line to the arduino. I also tried placing a bridge diode on the 48v then to the divider resistor, its linearity is way off. So I dont think that will work well.

Thanks for your inputs.
13  Forum 2005-2010 (read only) / Interfacing / Isolate ADC inputs on: September 20, 2010, 06:22:54 pm
Hi,

I need help isolating the ADC inputs. Here's what Im up against.

Im creating several LCD meters for a friend of mine to monitor voltages/current on his rack power equipment(telecom). It operates at 48v negative GND. So all is well and good up to this point, LCD meter working aok. But his equipment can be switched to handle 48v positive GND. With this scenario I could use a bridge diode to the supply of the uC to ensure that the + and - are always correct. My problem is the ADC should be able measure voltages on either GND orientations. Meaning some are +gnd and some are -gnd, so having an isolated power supply wont help. I've looked at the Ti INA117 differential opamp and use it as Differential to single ended ADC input buffer but dont know exactly how to use it (not to mention pricey).

So I think I have narrowed the solution(with my limited electronics knowledge)to having a differential input buffer to the ADC to isolate the monitored voltages but just dont know how to implement it.

All inputs are welcome.

Thanks
14  Forum 2005-2010 (read only) / Interfacing / Re: How can I measure AC voltage in the range 0-250 VA on: August 21, 2010, 10:54:08 pm
How about using a wallwart, linear type not switching then maybe a resistor divider on the secondary output.

Similar to what these guys did.

http://www.itwatchdogs.com/product-detail-city_power_monitor-20.html
15  Forum 2005-2010 (read only) / Interfacing / Driving solenoids. Please help on: March 15, 2007, 05:07:14 pm
Hi, I need help with something probably is very simple for you guys.

I need to drive 2 solenoids (24vdc, 2 amps), Ive been looking for a software controlled driver and found this device which looks like the product i need. Can someone please show me how it is connected, I looked at the tutorials but couldnt find anything similar. I just need to drive solenoid 1 for less than a second, turn it off, wait 1 second, turn on solenoid 2 for less than a second, turn it off, wait 1 second then it cycles again

Can the unit drive the solenoids directly?.

The code for the blinking LED seems like it just needs to modified a bit for it to be used in this application.

All suggestions and info are very welcome.

Thanks

Roy
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