LED (Light Emitting Diode) Information

Does anyone know where you can get a good L.E.D. that works wth the VEX system?

i am pretty sure that any LED will work whe plugged into the red and black slots on the digital IO ports.

I believe that other folks have discussed this in the past. Do a search and see what comes back.

I tried many searches in the past, but nothing came up.

I found a L.E.D. that works that only costs about $1.30 at RadioShack. It is a 2.1V | 25mA | 6.3mcd green L.E.D. Here is a link:
5mm Green LED. It’s product code is 276-022.

I’m working on a code for testing them, now.

FYI the only thing that determines whether or not an LED will work would be if the amount of volts it requires matches the amount put out by the M/C, and amps too.

**chee **- This advice isn’t up to your usual quality standards :slight_smile: … Saying that an electrical device needs to supplied the right current and voltage doesn’t convey much more information than simply saying it is an electrical device. :slight_smile:

However, I have gathered from other threads that one consequence of the way the Vex Microcontroller circuitry has been made compatible with a variety of typical sensor circuits; is that it is also LED-friendly.

Ryan - Try these URLs:


https://vexforum.com/t/leds/12442/1
https://vexforum.com/t/using-non-vex-parts/12567/1
https://vexforum.com/t/vex-blue/13752/1
http://www.vexfan.com/viewtopic.php?t=219&highlight=led
https://vexforum.com/t/answered-led-help/12440/1
[https://vexforum.com/t/answered-old-forum-data/12341/1

Some them should help you learn parts of your answer. Others of them should help you ask the right questions to fill in the gaps or parts that you don’t understand.

Blake](https://vexforum.com/t/answered-old-forum-data/12341/1)

Any Led Will Work, Besides The Jumbo Ones, I Havent Tested Them Yet.

All Other Leds Will Work When Wired Correctly!!!

Remember, short end is ground (black). I bypassed the controller completely when I used LEDs on my robot. I have a non-Vex limit switch that activates two LED’s in the back so that I can tell the arm is in position to pick up tubes off of the ground. I’m running off of a 9V battery and have to have a 1K resistor in between.

https://vexforum.com/t/leds/12442/1
https://vexforum.com/t/using-non-vex-parts/12567/1
https://vexforum.com/t/vex-blue/13752/1
http://www.vexfan.com/viewtopic.php?t=219&highlight=led
https://vexforum.com/t/answered-led-help/12440/1
[https://vexforum.com/t/answered-old-forum-data/12341/1

Some them should help you learn parts of your answer. Others of them should help you ask the right questions to fill in the gaps or parts that you don’t understand.

Blake](https://vexforum.com/t/answered-old-forum-data/12341/1)

that led friendly thing u said explains y a led i put in the vex motor slot to power it didnt burn out b/c i think the current was perfect

I don’t understand…the specs say that the max output current is 1ma, but people have had 25ma led’s working.

Anyway, can anybody just tell me if these leds are vex compatible?
(some text on this page is in Hebrew but the specs should be in English).
Also, will I be able to connect them straight to the RC or will I need to put in a resistor?

http://www.arihav.com/products/led/index.asp

Those LEDs will light up when connected to the Vex controller. They will not be as bright as their ratings, because you will not be suppying them with their full rated current.

The following image is from the Vexlabs download site (Sensor Test). It shows LEDS being plugged directly into digital ports with no resistor (There is already a 1K resistor inside the controller).
The LED should be plugged between the inside pin (signal) and the outside pin (ground). If you try to plug it across the center and outside terminals, you will supply 5v (digital connector) or 7.2V (motor connector) to the LED. This may not burn it out, but it will stress it (and possibly the RC) beyond its rated current.

https://vexforum.com/gallery/files/1/4/6/1/sensortest.jpg

Would it be possible to create a home made device that you could plug say 5 LED’s into but only take up 1 I/O slot on the VEX controller? But the hard art I am asking about, is making it so that only 1 to 2 LED’s are on at any given time. ie. if Arm is up Green turns on if Bumper switch is tripped yellow goes on, etc…

Any ideas? I can’t think of any way except pluging the home made device to the controller and then having an on board proccessor on the home made thing that can decide which output (on the home made device) to give power to, to turn on the LED. But that would be very complicated I think…

i got some cool cold cathodes from ozium.com that look great under a robot:)

it seems that they have moved websites…

It is possible, once you choose how (what protocol will you use) you will convey from the Microcontroller to the “device” which LEDs should be lit and which should be off.

There is no free lunch. You either send this information across more than one physical connection, or you need to spread the information out in time as you transmit it across a single connection.

Blake

It is possible to do this using one of the Vex serial ports hooked to a small microcontroller, which can then drive as many LEDs as you care to implement.

If you can live with using two Vex ports to drive 8 LEDs, then use a shift register like TPIC6B595 to accumulate 8 bits of data and drive the LEDs.

One port provides the sequential data bits to the SER IN pin, and the other tells the shift register when to advance by pulsing the SRCK pin. To program it, you have setup both as digital output ports, and then wiggle the port bits directly to change the LEDs:

Output state of LED7 to SER IN
Raise then lower SRCK (data is read by shift register)
Output state of LED6 to SER IN
Raise then lower SRCK (data is read by shift register)
...
Output state of LED1 to SER IN
Raise then lower SRCK (data is read by shift register)
Output state of LED0 to SER IN
Raise then lower SRCK (data is read by shift register)

Wire each LED(-) to the DRAIN0-7 output pins, and each LED(+) through an appropriate resistor (try 220 ohms) to the 5V power from the Vex. The LED state is ‘1’ for ON and ‘0’ for OFF.

You need a 3rd signal to drive the RCK pin, but you can derive it from one of the other signals at hand. You can invert SRCK to drive RCK, but you’ll have to add another chip to do that. Alternatively, if you are willing to only have 7 LEDs, just wire SER OUT to RCK and always output a ‘1’ for the state of LED7 in the sequence above.

Hope this helps,

  • Dean

Just so everyone knows, there are some cheap LEDs at RadioShack with built in resistors that you can just plug in.

i like the little tip i picked up from either Servo or HVWtech.com (i forget!), take some spare 220ohm resistors and some LED lights then just solder them together

save money and practice soldering, thats pretty much how i learned to solder