Sensors and costum circuits doubt
 

Hello partners, I´m in the team 5312 and we got some festo sensor, this guys give one signal back of 12 VDC, now we read the entire manual, but we didn´t find so much info about using this kind of sensors (inductive) and creating a custom circuit to transform 12 VDC to 5 VDC, if you can help us we will be so grateful.

Re: Sensors and costum circuits doubt
 

Hi Rafael,
I think most of your questions can be answered here: http://wpilib.screenstepslive.com/s/.../24166/c/86642

I think this is the specific page you want to look at:
http://wpilib.screenstepslive.com/s/...he-2015-system

Re: Sensors and costum circuits doubt
 

R30 Any active electrical item not explicitly listed in R18 or R55 is considered a CUSTOM CIRCUIT. CUSTOM CIRCUITS may not
produce voltages exceeding 24V.

R44 CUSTOM CIRCUITS shall not directly alter the power pathways between the ROBOT battery, PDP, motor controllers, relays,
motors, or other elements of the ROBOT control system (items explicitly mentioned in R55). Custom high impedance voltage
monitoring or low impedance current monitoring circuitry connected to the ROBOT’S electrical system is acceptable, if the



As long as you are within 24V and sourcing all voltage downstream from the Power Distribution Board (PDB), your circuit is legal. You can source 12V from the PDB for your sensor and use 5V logic for whatever you need.

Hope that helps.

Re: Sensors and costum circuits doubt
 

Thanks for the answer, well, not that pages doesnt answer actually, we get this sensors, http://www.festo.com/cat/es-ve_ve/da...ES/SIEX_ES.PDF
sorry if this is in spanish, we want this sensor, just that the manual doesn´t say anything about limitations about the use of sensors

Re: Sensors and costum circuits doubt
 

Thanks man, we want to built a regulator that take the 12 VDC signal from the sensor and regulate it to 5 so the roboRIO could use it

Re: Sensors and costum circuits doubt
 

Rafael,

Protecting a 5V input circuit from 12V can be pretty simple. The circuit below will limit the input voltage to the RoboRIO to just under 5V. As simple as it is, test it on the bench before you plug it into what may be your only RoboRIO.

Good Luck!



Disclaimer: Conceived at 6:30AM, pre-coffee.

Re: Sensors and costum circuits doubt
 

Most of the rules are restrictive/negative. Some rules explicitly requires a certain part or configuration (e.g. that you use the PDB, and power the Rio from this port, or that the motors be from the list). More common are rules that disallow certain items (the 24V rule, the hazardous materials rule, and the budgetary rules). Unless there is one of these rules that disallows your circuit one way or the other, you can use it. Unless it costs more than $400, has mercury, or needs 24+V, I can't think of many rules likely to exclude a proximity sensor.

Re: Sensors and costum circuits doubt
 

Raf,
You don't say whether you are using the PNP or the NPN part. If my translation of the manual is correct either of these devices will work down to 12 volts. (10-30 volts) Depending on which device you use will modify the circuit a bit. The interface shown above with the zener diode will work well for your application. You may also get goos results using a resistor voltage divider or a simple transistor switch as an output of the sensor you are planning. I would expect that the manufacturer would have an application note on interfacing these to a five volt system. Generally, NPN devices provide a closure to ground rather than a closure to power supply. These may be easier to interface than the PNP output.

Re: Sensors and costum circuits doubt
 

A separate caution about this sensor that you may have thought of already.
It will brownout when the robot battery voltage dips below 10v, as it will during a normal playing match.

You may want to give it regulated 12v power from a VRM.

Re: Sensors and costum circuits doubt
 

For a 12V NPN sensor, would you wire +/ground to the VRM and signal to a DIO on the Rio?