hi
currently im having a project with 36 buttons (with shift registers 74hc165) and 18 oled 1.3 screens, which are to much for the teensy (250ma current max) , i'm about 400ma now
my question is which device should i buy to work with external power that powers al the components and how shoud i hook it up?
the usb is used also from the teensy
Any device that takes its power from 5V or 3V3 ( depending on the processor ) can be powered by an eternal power supply. Simply connect the external +ve to what you would normally connect to the power output of the Teensy to the external power supply, and then connect the negative of the external supply to the ground of the Teensy.
The signals going to say an OLED display do not take more than a milliamp or so, they are not powering the display.
I bet you are not. How are you calculating this?
hi mike
the screens take about 11ma, so 11X18 = 198
i searched a lot about buttons and their draw and found less usefull things, something that came up is that a button can use 6ma (multiple treats found) so 36*6 = 216ma ==> but im not shure about this
so this are max ratings but i want to be safe, would a buck converter suffice? =
the power consumption of the shifts and teensy itself are not noticable
No they don't, not from the pins that drive them, but they might from the power connection. As I said these can be powered externally.
No what nonsense is this? A digital input is a very high impedance so takes almost no current, especially if you use the internal pull up resistors and wire the button between input and ground. With an internal pullup resistor being about 40K that means the push button will draw, 5V / 40K = 0.125 mA. But you can't just multiply this by a socking big number (216) because that is only the current they draw when they are pushed. When they are not pushed they draw almost nothing. So multiply 0.125 mA by the number of buttons you can push at any one time.
That buck converter, no matter what it says is unlikely to be able to supply much over 500mA. Basically they are useless in my experience.
As to the power supply you posted, It seems to be nothing more that a buck / boost converter, You still need to supply the actual power to it.
Anyway if you are serious about what you do, you shouldn't be using solderless bread board anyway.
Yes indeed from the power connection
so putting these on a different power suply and not from the teensy 3.3v would solve everything i think?
the buttons i wasnt shure like i said and didnt find enough valable info, i use 10k pulldown reistors feeded from the teensy so 3.3/10 = 0.33ma like you said when pulled. the max is 8 so this would make 2.64ma
A bad idea, as this configuration takes more current when pressed than the other configuration.
OP reads the buttons via HC165s. This has no internal pull-ups. There is probably no difference between pull-up and pull-down.
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