How to get the Analogue Outputs working on my K8055

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1

Hi

I’ve got all my digital outputs working by activating lights via external relays.

How can I get a set of lights (2 in total) to work from the analogue outputs (like dimmer light in the home) ?

2

There are several possible solutions.
If you are using low voltage DC lamp then you may use the PWM output of the K8055.
You need just one external power transistor to drive the lamp.

If you are using 230V AC lamp then one solution may be the K8064 - DC controlled dimmer.

3

Hi

Thank you, my long term aim will be to power main 240v lighting but currently I need just to be able to control a low voltage bulb - for example 12v.

Can you recommend a brand/model of external power transistor that I can use and how it should wired to the bulb/power and K8055 board ?

Thanks

4

If you are using max 20W lamp then you may use transistor TIP120, with a heat sink:
fairchildsemi.com/ds/TI%2FTIP122.pdf

The wiring is very simple:

800×361

5

Hi

With reference to the TIP120on the diagram can you confirm the following :

connection to the - on the battery is the base (pin 1)
connection from the PWM1 is the collector (pin 2)
and connection to the bulb is the emitter (pin 3)

6

just a quickie, what purpose does the 1k resistor serve ?

7

It is a pull-up resistor needed for the open collector PWM output.

8

I had the same question I used the above circuit diagram works kinda THANKS,

For a single LED I worked out that the LED requires 2-2.4v Forward voltage so 500ohm’s of resistance, placed the resistor before the bulb in the circuit 1.9-ish volts across the LED which I am happy with

My question is why is it when i increase the PWM output on the software the LED goes dimmer and off in the last 5% (5% bit I read about already) shouldn’t it be the other way around it increases the brightness when I increase the slider value on the software? Just wondering

Also what is the formula to work out how much resistance to use with LED if there is more than one? I use this one if there is one, and series vs parallel to get constant brightness across the LED’s
R=(VS-VLED)/ILED

And with the slider at about 90% the voltage only drops 0.5v to 1.4-ish volts across the LED I though it would of be more? 50% duty cycle 50% of the original voltage?

Thanks if anyone can answer some of my questions!

Ash

9

[quote]My question is why is it when i increase the PWM output on the software the LED goes dimmer and off in the last 5% (5% bit I read about already) shouldn’t it be the other way around it increases the brightness when I increase the slider value on the software? Just wondering[/quote]The PWM output of the K8055 is open collector output “active low”. The higher the PWM percentage value the longer time the output of the K8055 is low.

[quote]Also what is the formula to work out how much resistance to use with LED if there is more than one? I use this one if there is one, and series vs parallel to get constant brightness across the LED’s
R=(VS-VLED)/ILED[/quote]If you use more than one LED, connect all the LEDs in series, so only one resistor is needed for the string of LEDs. In the formula put VLED the sum of the voltages of all the LEDs.

10

Thanks for that,

That makes a bit more sense with a open collector, the formula is good as well but what if there are different colours? Connect the same colours in series and colours in parallel? As they would have different forward voltages.

How would that work on the same PWM output as before

11

[quote]Connect the same colours in series and colours in parallel? As they would have different forward voltages.[/quote]This is good idea. You need one resistor for each string of LEDs. You may balance the intensity of different colors by selecting proper resistor value for each color.