Quote:
Originally posted by Chipawa
Question for you all...We are trying to monitor our drive motor currents using LEM hall effect transducers. We are a rookie team and are following guidance from a white paper written by Steve Bunning, a mentor for Team 620.
The paper mentions powering the sensors from Pin 1 on the analog input to the robot controller. This pin is +5 v for "Gyro." The other 5v pins do not have sufficient drive to power the sensors. The analog input connector only has one pin for +5v for Gyro.
My question is how would we power multiple current sensors if there is only one pin that provides enough power for the sensors? Options that come to mind are to try the other 5v pins and see if they work, gang two wires off of pin1, or build some sort of custom circuit.
If anyone has had to deal with this, I'd appreciate any advice. Many thanks.
-Chip
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If you are going to exceed the current capacity of Pin1, you'll need to create a new +5V supply from the +12V Buss fuse panel.
IMO the easiest way is to create a 1A +5V supply off of the +12V is with a 7805 style three terminal voltage regulator. (Search for "7805" at
http://www.digikey.com, then select "voltage regulators", to see numerous brand options. A typical number is the Fairchild LM7805CT.) They are easy to use, and are internally current limited.
Buffer the +12V from the output of a "custom circuit" 20A breaker by first passing it through a 1A diode (such as a 1N4001 - 1N4004), then to a 100uf 25V capacitor to ground. This isolates you from motor noise. Now use the app note circuit to create your +5V at 1A supply.
Example - see:
http://rocky.digikey.com/scripts/Pro...261&M=LM7805CT )
Use the most basic "fixed voltage regulator" circuit on page 21, the chip itself and the pair of capacitors.
Notes:
1) Those small filter capacitors (.1uf - .33uf) on BOTH the input and output of the regulator to ground on this chip are important. They prevent high frequency oscillation. Even though you are using a 100uF capacitor, ALSO include the other small input cap.
2) If you choose a 1.5A version of the regulator instead of a 1A version, replace the 1N4001 blocking diode with one rated at
least 1.5A as well.
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3) Radio Shack carries this part as 276-1770.
4) You WILL need a heat sink for this item. Radio Shack also has the "TO-220 heat sink" and "heat sink grease" for it (and the small nut and bolt to tie them together in their hardware packs
)...
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Good luck!
- Keith