In order to power my servo and Photon I will supply a 7V 3A supply. The Servo draws maximum 2A. In order to step down the voltage to 5V to power the photon, I will apply a LF50CV TO-220 voltage regulator. The regulator outputs 5V @ 500mA, would this be a sufficient power supply for the Photon? I have read that maximum draw is 1A.
The photon will be powered 24/7 and the servo will only operate two times a day for ~5 seconds, thus being idle the rest of the day. I will add 220uf (or greater) capacitors for both the photon and servo in order to secure a stable supply.
chipmc, can you describe this a little more? I have an RC servo motor controlled by a photon. I am using an phone charger 5V/1.5A as a power supply with power running to both the Photon and the Servo on a prototype PCB I made. What should I be using to protect the Photon (capacitor, diode, ?) and where in the circuit should it be? Thanks
The answer will depend on how you are driving the servo motor. If you are using the Photon to control the motor through a motor driver board, like this one - you are all set as the driver board will take care of that.
You will want to put a couple capacitors (one one each side of the regulator as specified on page 5 of the data sheet you linked to .
If you were using the Photon to drive a spinning motor, you would want to put a diode between the power and ground such that is could protect the Photon from the reverse current once you stop powering the motor but this does not sound like your use case. If you are curious, here is a decent article the explains this concept:
I hope this is helpful. Good luck with your project and feel free to ask more questions as you go.
Chip,
I am using a typical hi torque RC servo that is connected to the same 5V power input from the 1.5A power supply that the Photon shares. The servo signal wire is hooked to pin A4 of the Photon, As I understand it there may be some back EMF from the servo that can harm the Photon, so that got my attention. I don’t believe I have so much an induction problem from a collapsing field (like in a solenoid) but if the servo is manually driven, I suppose it will act as a generator and produce back voltage that might damage the Photon since they are on the same power line. In that case, would the diode be placed in series on the servo 5V+ line so that no voltage can be fed back to the Photon? Is this accurate or do I misunderstand what is going on. Here is the schematic of my circuit
Thank you for your reply chipmc. The servo will be powered directly with the 7V 3A wall wart (with capacitors before and after). I will apply a 5V 1A regulator (7805ACTG) between the wall wart and the Photon. As the Photon itself does not power the servo, a flyback diode would not be neccessary.
Without seeing what the circuit you are controlling with that A4 pin, it is a bit hard to tell you the best course of action. There are some things you can do to protect your Photon but, which is best will depend, in part, on what protections are already in the motor controller your are connecting to. Here are some ideas, and perhaps you can take a look and share some more details as well:
A4 - GPIO pins can be protected a few different ways:
If you are worried that the device you are controlling might be misconfigured and the “signal” A4 is connected to is actively being high or low, you can insert a 1k resistor into the line. This is a cheap protection and will have little to no impact on the circuit if the “signal” is properly configured as a high-impedience input.
If you are worried about back-voltage that would go above 5V, you can insert a diode. Just make sure that the body voltage drop of the diode subtracted from 3.3V is over your motor controllers “high signal” state.
There are other techniques such as using an opto-isloator but this is likely overkill.
Don’t forget this from the Photon data sheet - “All pins except A3 and DAC are 5V tolerant (when not in analog mode). If used as a 5V input the pull-up/pull-down resistor must be disabled.”
To protect the Photon itself, you need to make sure it does not see big variations in voltage. Here are some basic protections:
Add a large cap after your regulator as specified in your data sheet.
You have already placed a power regulator between the wall wart and the Photon. It sounds like this will be a good solution. If you see issues, you can pick parts that have more protections built into the regulator. For example the (MIC29151-5.0WT) comes with an impressive list of protections: Over Current, Over Temperature, Reverse Polarity, Transient Voltage.
Sorry it took me so long to compose the response. It sounds like @Roheik has responded that you are good to go but I hope some of this is still helpful.
