Hello AAC Forum,

Thanks for the replies.

to djstantasi
The Ardunio, the PIR and the LEDs are powered by connection
to the power supply at the power board which is
connected at the node marked 'barrel jack to power'.
Its does not say it on the schematic but the
power supply is a regulated 5 volt 4 amp ac/dc
converter.

The barrel jack on an Arduino is designed for an input of 7-12 VDC. It is connected to an onboard linear regulator. If the LEDs load drop the input voltage, the Arduino may reset. Hence, it would be non-operational.

I believe you could connect the 5V to the 5V pin of the Arduino and bypass the linear regulator.

I based my earlier comments on your schematic, which showed the LEDs powered via the Arduino.

 

Hello djsfantasi and the AAC forum,

Thanks for the excellent comments on the power to the staircase system.
Not sure if it is realized that the barrel jack marked ' barrel jack to power' is a separate jack from the Arduino jack.

It is intended to power the Arduino from the power board to the 5v and grnd pins, but perhaps it would be better to
run a female plug to the Arduino barrel jack from the power board and take advantage of the Arudino's regulator.

Some how this thread got combined into a previous dialogue. So it is seen now that the power
supply has changed from earlier schematics.

Much obliged.

Allen in Dallas

 

I don't know anything about Arduino, so I can't touch that part of it. However, I do see you're powering an LED from a 5V source. ASSUMING you're attempting to light a single red LED, here's the breakdown of what you have set up:

5V (source) minus 1.8V (forward voltage drop of the LED) = 3.2V. Q1 will have a further drop of about 0.7V leaving 2.5V to work with. You have a 10Ω resistor in series with the LED and Q1. That gives you a working amperage of 0.25A (250 mA) FAR TOO MUCH for a single red LED.

Assuming all the same circumstances but using a super bright Blue LED, with a Vf of about 3.2V, that works out to 1.1 volts for the LED. Remember, I've had to subtract the Vf through the transistor as well. That's still 110 mA, again way too much for the LED.

Q1: You should push 1/10th of the current into the base of the transistor in order to turn it fully on at 250 mA or even at 110 mA. So, a resistor between the Arduino and Q1 should be (@250mA) 17.2Ω. (@110mA 39.1Ω). In your circuit, 470Ω is way too high to turn the transistor on in this case. Now - let me just say 'my skill level with transistor biasing is not the strongest. In fact, I wouldn't even use "strong" in the sentence.' So I may have my facts wrong. If so - someone will definitely correct me. I'm OK with constructive criticism. Sometimes that's a way to learn more. Learning from mistakes.

In your case, the failure of Q1 to turn on may have saved your LED.

OK, I'm back to keeping my mouth (keyboard) shut.

 

Hello djsfantasi and the AAC forum,

Thanks for the excellent comments on the power to the staircase system.
Not sure if it is realized that the barrel jack marked ' barrel jack to power' is a separate jack from the Arduino jack.

It is intended to power the Arduino from the power board to the 5v and grnd pins, but perhaps it would be better to
run a female plug to the Arduino barrel jack from the power board and take advantage of the Arudino's regulator.

Some how this thread got combined into a previous dialogue. So it is seen now that the power
supply has changed from earlier schematics.

Much obliged.

Allen in Dallas

To power the Arduino using its onboard regulator, you would connect 7-12V to Vin and connect ground. You don’t have to use the onboard barrel jack.

 

Late to the party, so this might already have been addressed. By my read, the LED datasheet does not state or imply any kind of internal current limiting. If so, then ...

The LED connections in posts 1, 12, and 16 will not work well. Each of these shows LEDs or strings of LEDs in direct parallel. Because the forward voltage Vf of a diode is not tightly controlled, LEDs with lower Vf will hog current away from ones with higher Vf. There is more than enough variation throughout a small batch to make a clearly visible difference. Post 15 shows the correct way to drive two or more strings of LEDs.

If the Vf really is above 3 V and you are stuck with a 5 V rail, then the only method for the 18 LEDs in post #16 is 18 resistors, one in series with each LED.

ak

 

@allenpitts

There are simpler ways to do this with RC circuits.... no MCU or Arduino necessary.