How to control and dim a 12V lamp with a BS2?

bees

Hello, I've got a question about digital to analog conversion with the BS2.

I'd like to use my BS2 to control a 12V lamp which will draw a max of 1.5A. I need to be able to dim it with moderate resolution, but I can't tie up the processor with PWM since I need to monitor some sensors while outputting the lamp setting.

I've designed a system that does what I want, but uses a servo mated to a dimmer rheostat. I'd like to get rid of this, and electronically control the brightness of the lamp.

I found the following N & V article helpful, it describes the creation of a D/A circuit : http://www.parallaxinc.com/dl/docs/cols/nv/vol2/col/nv59.pdf

The problem is that the above setup can only source 20mA, but I need considerably more than that.

Can anyone suggest an easy way to electronically dim my lamp, or perhaps a way to modify the above example to work for my needs?

Thanks!

Martin Hebel

The "Process Control" text from Parallax has a circuit driving a fan at variable speeds that does not tie up the processor.· Using a transistor of sufficient current capacity, it should be able to be modified to drive your lamp.

http://www.parallax.com/detail.asp?product_id=122-28176

-Martin



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StampPlot - GUI and Plotting, and XBee Wireless Adapters
Southern Illinois University Carbondale, Electronic Systems Technologies

bees

Any recommendations for a transistor which can handle 1.5A max at 12V?

Phil Pilgrim (PhiPi)

The circuits shown in the book, even though they use the Stamp's PWM output for regulating fan speed, operate the drive transistor in the linear region. When driving a 12V lamp at 1.5A in this manner, your drive transistor is going to dissipate a lot of heat. A better solution would be to pulse-width modulate the lamp itself, using a logic MOSFET like the IRLZ14. A constant PWM output for driving the MOSFET can be obtained from either the PWM Pal or the MoBoStamp-pe.

-Phil

bees

Phil, great idea, that's what I'm looking for. I notice that Parallax appears to carry the IRL520 at

http://www.parallax.com/detail.asp?product_id=604-00039

but I can't add it to a cart. Has it been discontinued, site admins?