Setting up LEDs on Timer + Dimmer circuit, help needed

[BeanAnimal]

Let us know how things go. I just got new hardware in the mail yesterday. I am still waiting on some I2C DACs and Digital Pots....

BTW here is a nice little PWM to voltage or current source
http://www.piclist.com/techref/microchip/aout.htm

[ronjeremy311]

Originally posted by RyanBrucks
thanks for clarifying.

I ordered a RCM4010 RabbitCore. $99 bucks for the chip and the dev tools is a pretty good deal.

I ordered an AVR Butterfly, Carrier, and programming book from Smileymicros yesterday. So maybe we'll come out of this with at least 2 ways to skin this particular cat.

Since I am not trying dim as big a load as you Ryan, some of the guys on the AVR forum also pointed out that I could get away with using a regular NPN transistor. I was also told that an IRF510 Mosfet (which I was told is available at RadioShack) could be driven directly by the controller. Not sure how much current it can switch though, I haven't looked at the data sheet.

[RyanBrucks]

Looks like the IRF510 would work too. the gate voltage threshold is 2-4V, and it can handle 4amps continuous, and 100V Drain-to-Source.

Can somebody explain exactly what 'Breakdown Voltage' is? Is it a kind of minimum voltage required to run through the mosfet? It's listed at 60. So many stats I can't read

[BeanAnimal]

The breakdown voltage of a transistor is the voltage at which the diode will conduct current in the wrong direction. In other words if you over bias the transistor (in this case by more than 60V) then the transistor will avalanche and allow current to flow in the wrong direction.

Forget transistors... thing of a diode. It stops current in one direction. If you bias it enough it WILL conduct in that direction. A zener diode will do so without burning out.

Look at it from a mechanical perspective. If you put to much reverse pressure on a check valve, it will leak a little. At some point it will give way and allow ALL of the pressure to go the wrong direction.

[BeanAnimal]

http://ece-www.colorado.edu/~bart/bo...ter4/ch4_5.htm

That may help you

[stugray]

RyanBrucks,

Any luck yet? I just ordered the RCM4010 myself. I plan on experimenting with the LED dimmer and variaable speed AC motor speed controller.

Stu

[RyanBrucks]

Hey guys,

I received the RCM4010 and two different mosfets, the IRF3708 and the IRF510. I think the 510 will be better suited for the LED application.

I haven't had any time to experiment with any of it though. Right now I'm writing from Hayden Lake, North Idaho, on a really old PC with AOL (gasp) and a modem (GASP!!!! I'm here visiting family.

Before leaving, I finished my 4 acrylic tanks (RO, mixing, frag and fuge), and a sump/refugium tank for my sister, so I was way too busy to get to this yet.

I get home wednesday night, and I am on vacation from work until the 2nd!!!!! This *should* give me plenty of time to build my garage stand, get an electrician to do some work, and mess with the rabbitcore.

I will also post a diagram of exactly how I plan to wire the mosfets before I do anything. I need more confirmation than just an engineering diagram sometimes hehe

stu,
I'm very interested to see what you can do with the AC motor. These rabbitcores have alot of PWM, and I have alot of mosfets

[RyanBrucks]

Can I get you guys to check over this 'non-diagram-diagram' for me ??? I say non-diagram because it relies on pictures instead of any symbols that might cause confusion for somebody like me.




I was a little confused about how the wire the gate of the mosfet. Part of my brain wants to think that the PWM actually connects to the flange, and not the gate pin itself. Also part of my is still thinking that the source should be connected to ground, with the + voltage connected inline with the LEDs to the drain.

Is the picture right?

(oh ya, check out how my garage stand is coming in this thread http://archive.reefcentral.com/forum...6#post11502756 )

[stugray]

RyanBrucks,

You need to hook it up differently. The + on the Power supply needs to go to the + of the LED strip. The return (-) from the LED strip connects to the Drain of the MOSFET ( with this FET consider the Drain to be the IN ). The Source of the MOSFET ( The OUT ) connects to the negative of the power supply (-).

Depending on the strip you have you might need the current limiting resistor in my diagram to guarantee that you dont supply too much current to the LED strip from your 13.5V power supply.

You also need a ground reference from the proto board to the power supply. Connect header pin 2 ( GND ) to the power supply - and the MOSFET should work..



I have my RCM4010 working and I am just beginning to try the PWM. I should have the code working with a IRF510 any day now.

Did you get the 'browseled' program to work yet? If you have gotten that far, you are doing great!

Stu

[stugray]

OH!! and I forgot to mention that I just got my free CREE XR-E LED in the mail today!

Time to play....

Stu

[RyanBrucks]

Wow thanks for catching those mistakes!

I must have been thinking that the mosfet 'stopped power from getting TO the LEDs', when in reality I suppose its just stopping the flow of electricity from making it BACK to the - power source.


what was mostly throwing me off is that on the diagram, the drain is pointing to "+ supply voltage", so I assumed that meant + on the power supply, and not - on the LEDs. Still thrown by that even after the clarification hehehe. Is it that the - from LEDs is still + supply voltage in the sense that that its merely a 1-way flow through the mosfet?


haven't gotten the test program running yet, but I got all my software installed and the chip mounted on the protoboard etc. Also looked over some docs and the big datasheet that lists the registers and all the default operating modes that need to be iniated etc. going to be more work than I thought (of course), but its really interesting. once the unit is configured the possibilities are endless. looking forward to the day when I know enough to program a touchscreen

[stugray]

Think of your MOSFET ( IRF510 N-channel ) as a low side valve. It controls the flow of electrons AFTER it goes through your load ( the LED strip ).

The other kind of MOSFET ( IRF 511 P-channel ) is a high side valve. It controls the flow of electrons BEFORE it goes into the load.

They both work in our application, it is just harder to turn on/off the HIGH side fet when using logic that is referenced to GND. The IRF510 is a low side FET.

Also.... I ordered a serial driven LCD ( from MOUSER electronics for ~$9 ) that should also be here this weekend, so I should have that working soon as well.

Stu

[RyanBrucks]

serial LEDs eh? nice. will you be able to directly control that from the rabbit, or are you using that for your PC?

[stugray]

I was talking about a LCD display screen for the rabbit.

It hooks to one of the serial ports and display characters numbers symbols, etc.

Stu