I would buy the 3A power supply.
Does the diode have to be a 1N5802
It needs to be a schottky diode. A 1N5820 would be best, Jaycar has them.
The capacitor is there for additional power supply filtering
Not always.
The ones with USB-A socket are.
Thanks jim
The LDR should be powered from the 5volt pin of the Nano.
Only the LEDs should get direct power from the external supply.
Leo..
Ok. Could you explain why that is?
Supply variations between external and Nano 5volt will also show up in the LDR value, which you likely don't want.
Leo..
Ok thanks. Then that goes back to my earlier question - would it be better to put the diode and capacitor closer to the power supply? Then those supply variations are smoothed out for the other ICs as well (the two TLC59116 and I also have some more LEDs driven by other ICs that I didn't yet add to the schematic diagram).
Smoothing capacitors belong near the load.
It does not matter where a diode is located when in series with a power wire.
Leo..
Cheers
What is the distance between the power connector and the Arduino 5V pin?
It would be somewhere from 2 to 10cm. But I'm not talking physical distance, I mean in the circuit diagram. Wawa already answered that question regarding the diode and capacitor.
But he was wrong.
The diode should only be supplying power to the Nano 5V pin like I show in my schematic.
Do not connect anything else to the Nano 5V pin
It's the physical distance that's important. More exactly: it's the resistance and induction of the connecting wire or PCB track that's important. Even if the power source is ideal, your device uses a variable current (inevitable for digital circuitry) which causes voltage spikes that will be transported to other devices. The trick is to short-circuit the high frequencies of those spikes as close to their source as possible. Hence the advice to put decoupling capacitors close to the pins of a chip or device.
D1 in post #25 will prevent the feeding of the LED strips from USB power when external power is absent. C1 can be omitted (the Nano board has its own capacitors) while capacitors near the driver chips will be useful.
The general advice is to never feed anything from your Arduino (but the examples on the website show it is done anyway). This advice is for beginners who think "my project is a small one, it's got only 1 motor" (or in your case: only 2 strips). It is quite possible if you know what you're doing, i.e. you need a certain level of knowledge in electronics.
The GPS may need more current than your board can provide.
Those opto isolators do not provide and isolation from anything or even do anything at all
Ok I understand.
Nah, it only requires 25mA max (see here).
I already explained what they are for in a post above.
That is not the purpose of the diode.
Please don't modify my circuit, please keep the capacitor.
Please follow my instructions.
It seem that most people here on the forum don't understand the purpose of the diode and capacitor.
Please show an updated schematic if you have one.
Hi jim
I have not modified the schematic from what you originally posted, I still have both the diode and capacitor in the place you said.
So if the diode is not to prevent current flowing from the 5V pin, then what is it's purpose?
So please explain, because drawing too much current through the Nano seems to be the main problem.
I would
- Separate LED power from Arduino power.
- Power the LEDs (not the LED drivers) directly with external 5volt.
- Use a small Schottky diode (1N5819) between external 5V and Nano 5V (cathode to Nano), to power the Nano if USB power is absent.
- Maybe a 47uF cap on the LED side of the diode.
That way USB power only powers the Nano, not the heavier LED load.
Leo..