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Transistor issues??

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Re: Transistor issues??

Postby Savage///Circuits » Thu Jan 27, 2022 11:19 pm

I still have those bi-color LED Bar Graph displays I bought. Did you still need help with switching colors between red / green?
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Re: Transistor issues??

Postby jknightandkarr » Fri Jan 28, 2022 7:44 pm

Maybe with using a single pin high on one n low for the other. Was thinking of a pnp & npn transistors with base pins connected togeather through a resistor. What do you think?
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Re: Transistor issues??

Postby Savage///Circuits » Sun Jan 30, 2022 1:52 am

I may be wrong, but you may be overcomplicating things. That is to say, NPN and PNP transistors work differently. You can use two PNP transistors or two P-channel FETs with an inverter (a single NPN transistor). You need to be able to switch the max current expected in bar mode. I don't remember how much current my circuits drew. I would really need to rebuild them.

Do you have a schematic for the board you showed? I could build part of that to test the circuit.
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Re: Transistor issues??

Postby jknightandkarr » Mon Jan 31, 2022 5:30 pm

Savage///Circuits wrote:I may be wrong, but you may be overcomplicating things. That is to say, NPN and PNP transistors work differently. You can use two PNP transistors or two P-channel FETs with an inverter (a single NPN transistor). You need to be able to switch the max current expected in bar mode. I don't remember how much current my circuits drew. I would really need to rebuild them.

Do you have a schematic for the board you showed? I could build part of that to test the circuit.

Ok Chris, I attached quick simple schematic. It has Q1-8 for all the Yellow LEDs (KARR), instead of attaching all in the circuit, and Q9-18 for the Red LEDs (KITT). Reason I was thinking of a PNP & a NPN is using a single common pin for the version selector. High for KITT & Low for KARR. This way it's not possible for both sides to be on at once. R19-23 can be adjusted as needed along with R9-18 for KITT's display since its LED in each has a LED pattern of 2-2-6-6-6-6-6-6-4-4 so the 2's need one value, 6's another value and 4's a different resistor value to make sure all the LED's are equal brightness. Since KARR's display always uses 6 LEDs per segment, this obviously only needs one value for each segment. I will probly increase the +5V to +12V and just need to adjust the all of the resistor values as needed. R20 & R21 are for the individual inputs for the actual LED driver for my Arduino Uno. I got lazy n didn't feel like changing them, so that's why there isn't a connection on them. LOL
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Re: Transistor issues??

Postby Savage///Circuits » Fri Feb 04, 2022 6:56 pm

Have you tested your switching circuit?

Also, why does each LED have a transistor? Are you no longer using the LM3914?
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Re: Transistor issues??

Postby jknightandkarr » Sat Feb 05, 2022 12:44 am

Savage///Circuits wrote:Have you tested your switching circuit?

Also, why does each LED have a transistor? Are you no longer using the LM3914?

Not yet i haven't but want to, been busy at work and either tired or sick lately. As for the transistors, I was expecting min 50 mA and 150 mA max per segment, so wanted to avoid damage, so thats why I have the transistors in. Since I got an Arduino Uno to work as the driver, I am going to try and avoid using one for this, as I need a microcontroller for the 8 LEDs on the sides and the 3 sets under the voice display anyhow, so I figured I could do it with an Arduino. After some searches, I found a project from Element 14, that did the job.

Here is a quick link of what all my display will do as far as the voice box goes.
https://youtu.be/rfAGfi5zqUk
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Re: Transistor issues??

Postby Savage///Circuits » Sun Feb 06, 2022 12:58 am

I didn't see the voice module active in that video. When I originally ordered the displays you were using the LM3914, so that's what I started my test circuit around. The outputs are current controlled on that IC and do not require transistors or even resistors. You can use an MCU, but I would still be doing it using the LM3914, myself.
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Re: Transistor issues??

Postby jknightandkarr » Sun Feb 06, 2022 11:15 pm

I didn't have one posted, just video of the MCU testing stuff, but here is a video of it working. I will have to try using 3914 again, couldn't get it working the first time for some reason.

https://youtu.be/35riTTwJGH0
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Re: Transistor issues??

Postby Savage///Circuits » Mon Feb 07, 2022 3:08 am

I don't know if I have any LM3914 chips currently. I am starting over...I do have the displays though and I can try this week to make the switching circuit for the red/green. It uses 3 NPN transistors to select using one I/O pin. Which color should be the default (I/O pin low)?
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Re: Transistor issues??

Postby jknightandkarr » Tue Feb 08, 2022 10:41 pm

It don't matter really, either one is fine.
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