I have a project involving 20 LEDs and a stepper motor controlled by a Leonardo.
With the Mux Shield II it will be physically possible to connect the 20 LEDs and a stepper motor driver (Easy Driver), but will enough power be available?
The Leonardo can supply a maximum of 200mA when powered by USB. Powering 20 LEDs alone will draw 400mA (assuming 20mA draw per LED). It is really possible to individually control and light up 20 LEDs (and the Easy Driver) using the Mux Shield II? Does the use of muxes and shift registers somehow make this possible power-wise?
If it’s not possible to have all 20 LEDs lit at the same would it be possible to have 20 LEDs connected but only light a fraction of them (4 or 5) at the same time? I guess what I am getting at in this is: is any power drawn by a pin that is LOW?
Sparkr:
With the Mux Shield II it will be physically possible to connect the 20 LEDs and a stepper motor driver (Easy Driver), but will enough power be available?
No and you answered your own question as to why.
Sparkr:
If it’s not possible to have all 20 LEDs lit at the same would it be possible to have 20 LEDs connected but only light a fraction of them (4 or 5) at the same time? I guess what I am getting at in this is: is any power drawn by a pin that is LOW?
Yes you can drive a fraction of the LEDs and have the rest in an 'off' state. There are 3 constraints that I can see.
1 - each 595 is limited to 70 mA max from it’s Vcc pin. So that’s no more than 3 or 4 LEDs on per shift register.
2 - there’s a total current limit set by the Arduino voltage regulator (as you already know).
3 - there’s a thermal limit to the Arduino regulator. Depending on how well it’s heat sunk and the input voltage, you may hit that limit before the current limit.
Of course 2 and 3 only apply if you’re using the barrel jack for power. Using the USB generally limits you to 500 mA. And I assume the stepper motor power comes from unmentioned power supply.
Mee_n_Mac, thanks for the reply. Thanks also for the data on the 595s–it gives me a better understanding of how far I might be able to push things.
I’ve been searching all over for some way to read the mA drawn by any given pin, but so far I’ve not found anything concrete. Is there a (simple) way to measure this either through code or a multimeter?
I plan on using the Easy Driver to drive the motor, and as you correctly assumed, the motor itself with be powered independently.
If I use the barrel jack for power, would the Arduino be capable of supplying ~900 mA when powered with ~7v as [this page suggests? I realize that the 595s will limit what I can power through the Mux Shield, but connecting the Easy Driver to the unused pins on the Arduino may give me more flexibility on how I use the Mux pins.
Pushing the idea of reading the mA used on a given pin just a bit further: Is there code out there to read the total mA drawn by the Arduino? I tried reading the mA of the Arduino using the setup found on [this page, but for some reason, my multimeter didn’t read the mA drawn. With the multimeter in series, the mA reading was at 0 and the Arduino wasn’t getting power. After taking the multimeter out of the circuit, the Arduino worked fine. I know the multimeter works fine, so I’m at a loss as to why the ‘in-series’ reading didn’t work.
Sparkr:
Is there a (simple) way to measure this either through code or a multimeter?
There's no current measuring devices onboard the Leonardo so there's no way to do it via code alone. A DMM/ammeter is the way. Simple ... that's a judgement call.
Sparkr:
If I use the barrel jack for power, would the Arduino be capable of supplying ~900 mA when powered with ~7v as [this page suggests? I realize that the 595s will limit what I can power through the Mux Shield, but connecting the Easy Driver to the unused pins on the Arduino may give me more flexibility on how I use the Mux pins.[/quote]
I thought that the 200 mA, mentioned above, was that number but as I look at the schematic I see that the Leonardo has a nominal 1A 5V regulator. So yes 900 mA seems a reasonable number.
Sparkr:
Is there code out there to read the total mA drawn by the Arduino? I tried reading the mA of the Arduino using the setup found on [this page, but for some reason, my multimeter didn’t read the mA drawn. With the multimeter in series, the mA reading was at 0 and the Arduino wasn’t getting power. [/quote]
As stated above, not by code alone. From your description it sounds like your DMM didn’t get switched into ammeter mode, thus no power got to the Leonardo. On some DMMs you need to switch the DMM leads to go into the DMM at different jacks. Read the manual and try again.
Mee_n_Mac:
From your description it sounds like your DMM didn’t get switched into ammeter mode, thus no power got to the Leonardo. On some DMMs you need to switch the DMM leads to go into the DMM at different jacks. Read the manual and try again.
The manual did indeed help :oops: and I eventually got the mA reading to work … as a bonus, I discovered that one of the fuses in the (practically new) multimeter was blown!
Mee_n_Mac:
I thought that the 200 mA, mentioned above, was that number but as I look at the schematic I see that the Leonardo has a nominal 1A 5V regulator. So yes 900 mA seems a reasonable number.
Thanks for confirming this via the schematic. I’ve seen much confusion on this matter and its good to know that the schematic backs up the 900 mA.
not to blow out the chip, and it would be nice to have some idea of how many mA my setup is drawing before I use too many pins.](