Converting a 12V led signal to 5V

[berkshirebugsy]

Hi All. I've noticed some signal kits available on various sites that stipulate 12v supply - and I quite like these but want to operate from the 5v outputs of an Arduino. is this possible?

The 4 aspect kit is supplied with a 10K resistor which (i believe) wires to the common anode of the LEDS.

Is it possible by changing the value of this resistor to get it to work from 5V?

Thanks in advance

Dave

[Brian]

Hi
Assuming the signals are lit by LEDs, 10K (10,000 Ohm) is quite high! Are you sure its not 1K (1,000 Ohm)? 1K is the more usual resistance for LEDs on 12 volts DC. Eckon / Berko are one such supplier who use 1K resistor. They AFAIK always use common Cathode (Negative).

A four aspect signal would normally use two resistors. One shared for the Red, Yellow and Green aspects while the second resistor is in the Top Yellow aspect.

Yes, you can reduce the resistor Ohm value for 5 volt operation and by using this web site you can get the minimum Ohm value recommend.. http://www.hebeiltd.com.cn/calculator/v5/led.php For ease of use Red/Yellow and Green LEDs are roughly 2.2volts and 10 milliamp is about the maximum current I would look for the circuit to consume (less is better!)
Using the calculator - Supply Voltage is 5.0. Diode Forward Voltage is 2.2. Diode Forward Current in ma is say 10. Number of LEDs is 1. The answer comes back as use a 330R (330 Ohm) resistor. Of course you can lower the current by increasing the resistance and see what happens and about 5ma is about as low as I would go. Higher resistance values will dim the LED, until you eventually reach a value where the LED cant illuminate.

[berkshirebugsy]

Hi
Assuming the signals are lit by LEDs, 10K (10,000 Ohm) is quite high! Are you sure its not 1K (1,000 Ohm)? 1K is the more usual resistance for LEDs on 12 volts DC. Eckon / Berko are one such supplier who use 1K resistor. They AFAIK always use common Cathode (Negative).

A four aspect signal would normally use two resistors. One shared for the Red, Yellow and Green aspects while the second resistor is in the Top Yellow aspect.

Yes, you can reduce the resistor Ohm value for 5 volt operation and by using this web site you can get the minimum Ohm value recommend.. http://www.hebeiltd.com.cn/calculator/v5/led.php For ease of use Red/Yellow and Green LEDs are roughly 2.2volts and 10 milliamp is about the maximum current I would look for the circuit to consume (less is better!)
Using the calculator - Supply Voltage is 5.0. Diode Forward Voltage is 2.2. Diode Forward Current in ma is say 10. Number of LEDs is 1. The answer comes back as use a 330R (330 Ohm) resistor. Of course you can lower the current by increasing the resistance and see what happens and about 5ma is about as low as I would go. Higher resistance values will dim the LED, until you eventually reach a value where the LED cant illuminate.

Thanks Brian - you spotted my deliberate mistake It is a 1k (I was rusty on my resistor colour codes.) The signals are Eckon (I'm just trying one out) and as you say they use a common cathode and supply a 1k resistor. I think in experimenting with other LEDs I have used 330R with success.

Many thanks again,

[Brian]

Hi
As the signals are Eckon, unless they have changed their wiring, each LED has its own Anode and Cathode wires running down the post.
Common Cathode just needs all the Cathode wires joined together and each aspect Anode is switched indivually.
Common Anode needs all the Anode wires joined together and the Cathodes switched individually.