Driving high currect DC LEDs

[Tim P.]

I am going to be driving (6) LED strips, each draws about 550mA @12V.

I see there is some talk about a modification of the FC board to do such a thing.

Excuse my lack of electronics experience if this is completely wrong, but could I use Crydom SSRs (DO061A) connected to the p0-p5 headers?

I was thinking I could cut (3) of the extension cables in half, solder to leads to the DO061As gate (proper terminology, I believe?) then connect the LED strips to the ssr's.  The SSRs appear to handle the voltages/currents appropriately and less than the 20mA per TTL pin.

I think this can be done with less expensive relays, but if I want the dimming I need to use the SSRs.

Am I on the correct track?

Thanks in Advance,

Tim

[JonnyMac]

I have on my list of possible project something called the HC-8 which would use eight TIP120 Darlingtons instead of one ULN2803.  The TIP120 is capable of 5 amps at up to 60 volts.  In the meantime, you can "roll your own" with this simple interface: connect to the Px pins:



Note that I don't have a value for the LED's resistor because I don't know what you have for V+ or the LED forward voltage (Vf).

The TIP120 is about $1 -- so it will be cheaper than using SSRs.  And... you can still use the PWM statement in the Prop-1 or Prop-2 to ramp the brightness up or down; if you connect to a Prop-SX you could do sophisticated background dimming (the FC-4 uses an SX processor).

[Bill P]

Jon:

If the LED were taken out of the circuit could another device be inserted such as a solenoid be used as long at it operated within the parameters of 5amps @ 60 VDC?  Would a blocking diode be used (1N100x)?

Just curious,

Bill

[JonnyMac]

Yes, if you're going to use an inductive device (anything with a coil) be sure to add a flyback diode; use a 1N4001 or better.

[Tim P.]

Thanks for the prompt reply Jon!

I've never done any electronic assembly before.  I understand the diagram, and I understand Ohm's Law, so I can calculate the proper resistor.

Any suggestions on how I could mount all this so I can solder the components together?  I see breadboards, which seem to be more suitable for a testbed.  I would like to make this as small as possible, without having my own pcb's made.

I played with the Prop-1 last night for the first time, I love it!  I can see where the Prop-2 has some programming advantages (notably gosub and the ability to toggle a variable), but nothing I couldn't overcome.  Each controller definitely has it's niche.  The prop-1 is great for me.

Thanks again for the help and the great product,
Tim

[JonnyMac]

I'm old and cranky so I don't do anything point-to-point anymore -- ExpressPCB is my friend; it doesn't take long to layout a circuit board, the cost isn't bad, and I can get dupes any time I need them.  If you're good with a soldering iron, p-to-p is the way to go.

The BS2 came well after people like me (I was an early adopter) had expressed long wish-lists to Parallax so, yes, it is a little easier to program.  That said, I absolutely agree with your point: every controller has a place and the BS1 is a great little controller.