Hi, i need your advice - knowledge
i have this display module that works with 24v dc
it takes +/- 24v dc to the 2 terminals and then in order to display numbers and the arrows i have to supply -24v to the terminals (A,B,C,D for numbers and to the 2 terminals for arrows)
one option is to pass the -24v from 6 relays and drive them from arduino
is any other option to achieve that ? are any Ic's that can do that instead of using relay modules
thanks in advance
I think it's a bit easier. You have to supply 0V using the 24V - as common Gnd.
Which voltage do you measure on the terminals?
FETs or bipolar transistors - with some level shifting. Optocouplers.
These may be easier than the relays.
I am sure other will come along with other suggestions or ask for more details.
This is a non-sequitur. +/- needs three connections giving a positive voltage referenced to ground and a negative voltage referenced to ground.
Two terminals probably means a DC voltage, and the "-" is probably ground on the board.
You generally want to avoid switching grounds since most components use the ground as a reference point.
What does the 12/24V jumper do?
Again- confusing. Where are you getting the -24V?
I suspect that this is just a DC power source and what you are calling -24V is simply ground. The - side of the supply. If I am right, then grounding any of the inputs will light a segment of the display. If this is correct then what is the voltage measured at A,B,C and D? If it's +5V then you can just wire them directly to the Arduino GIO pin.
If you don't have a voltmeter or DVM, then put the project back on the shelf until you do.
How do you know that?
My mistake ... yes with -24v i was referring to the ground (+ - ) power supply terminals .
i asked my friend that gave me this module and told me that was from an elevator cabin.
the elevator control has terminals with A,B,C,D ( and arrows) to display the floor when connect this module to them.
He told me that the 12v/24v jumper is because some elevator control manufactures uses 12v dc and some others 24v dc and so when you order the button panel for the cabin they prepare the displays depending the control voltage
i connect my multi-meter one probe to the ground and the other one to the (ABCD,Arrows) terminals and i got a reading of a 4v dc in every one of them.
if i ground any of the terminals then the display shows the number or the arrow (depending which terminal i am grounding)
i want to use it with a Arduino pro mini 8Mhz that is 3.3v tolerance
Then the pins should be compatible with 5V logic.
yes but as i want to use them with 3.3v logic i decide to use a darlinghton array ic like ULN 2803A
Should i combine it with Optocouplers for more protection to IO pins or using it allone would be fine ?
From what I have read here, I cannot see any need for an optocoupler.
Since you are only pulling a few mA (measure it) to ground, just use an NPN transistor like the 2N2222.
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