When I'm using a 12v 1000MA wall power supply on my breadboard arduino through a 7805 voltage regulator I can communicate with serial just fine, but when I connect my arduino to a DC/DC buck convertor that's being powered by a 36v DC transformer set at 12v out to the 7805 voltage regulator I get garbled serial data. I've read up on these DC/DC Convertors and they seem noisy. I have a 10uf capacitor before and after my 7805 regulator. Is there any other way to clean up the power? maybe use a bigger capacitor before the regulator?
my setup goes like this
120V to 36VDC Transformer (to high power LED's) to DC/DC Buck Convertor (to power 12v fans and arduino) to 7805 regulator to arduino
and yes, I've disconnected the LED's and Fans for testing, I still get a messed up serial output.
Switching regulators and linear regulators can sometimes play havoc with each other. The noise of the switcher can cause the linear to oscillate.
More capacitors are always good - you want low ESR to get the noise away as best you can. Also maybe a common mode choke on the input between the switcher and the linear might help (could be as simple as a ferrite ring with the wires wound round it a few times).
Perhaps you have a ground loop? The 36VDC power supply may have its negative output grounded, and the 12V wall wart may have had its output isolated from ground. If that is the case, and the device attached to the serial port is grounded (e.g. a PC, or a laptop running off mains power), then you have a ground loop when running from the 36V supply but not when running from the 12V supply; and a ground loop is likely to mess up serial communication.
You mention a transformer a couple times. Is there really a transformer (wire would), or was that just a term?
Yes, more capacitors, some smaller, some larger values would be good. Don't run other wires close to a transformer.
dc42:
Perhaps you have a ground loop? The 36VDC power supply may have its negative output grounded, and the 12V wall wart may have had its output isolated from ground. If that is the case, and the device attached to the serial port is grounded (e.g. a PC, or a laptop running off mains power), then you have a ground loop when running from the 36V supply but not when running from the 12V supply; and a ground loop is likely to mess up serial communication.
sorry for the delay in responding, it's been a busy few days.
That does make sense. If the negative of the 120vAC to 36VDC power supply is grounded, then the 12v coming out of the DC/DC Convertor does not have it's -12vDC grounded. So I should run a wire to the negative ground of the 36V Transformer to the negative of the 12v supply coming out of the dc/dc convertor?
I think the transformer case is grounded to the frame of the box which it's attached to, which is grounded to the 120v main power.
I have a 10uf capacitor before and after my 7805 regulator.
Do you have a .1uF from the 7805 input to ground (adjacent to the regulator)?
Show us a picture of your wiring.
Sorry, I don't have a picture at the moment, but my board is setup exactly like this
except where the 2 power connections are going to the 7805 regulator, it's just connected to the DC/DC Convertor to power it. So I should have a 0.1uf cap going from the negative of the 7805 to a ground source? which would be the case that the 36v power supply is housed in.
edit: now that I think about it, I do have the 36vdc negative connected to the 12v negative because I'm using a TIP120 transistor to control a 36v output (high power led), I can separate these with a 0.1uf cap if possible? And I'll check, but I'm sure the 36V is grounded to the power supply case, which is grounded to the 120v ground.
The caps should not be hooked from one ground to another ground. They should be hooked between ground and the positive voltage.
The grounds should be hooked together with wire.
120V to 36VDC Transformer (to high power LED's) to DC/DC Buck Convertor (to power 12v fans and arduino) to 7805 regulator to arduino
Hi, question, the 36Vdc power supply, is it pure DC.
Can you check the following with a DMM.
Measure the output voltage of the 36V supply with the DMM in DC Volt mode, it should read 36Vdc.
Measure the output voltage of the 36V supply with the DMM in AC Volt mode.
You should have 0.1 Vac or there abouts.
If its more like 18Vac then your supply is unsmoothed, it is producing ripple that is not helping the DC-DC Coverter..
The supply should consist of transformer, rectifier and capacitors, say 4700uF in value.
Only a thought, that no one has asked.
