Switching on a bank of leds

gchrt

Hi,

I am building my first electronics project. It is a miniature garage as an art project. When a person is near the garage the door rolls up and the interior lights come on revealing what is inside. The program works well, the step motor turns and the one led for testing comes on. My intent is to have four lighting units in the garage each holding 6-8 leds.

Question #1 is how best to turn on this bank of lights from the Basic Stamp. Which is intimately related to Question #2 - how best to lay out the bank of lights. I was thinking maybe each unit's led in series and the four units hooked up in parallel just to accommodate the power.
Speaking of power it looks like the Stamp hasn't the power for these lights and I guess I need to build a separate circuit with its own power to run just the lights. Not sure how to approach building this plus having the Stamp turn them on.

I've researched this and found many options (switching IC's, Darlington's, relays) that sort of addressed my needs but I'm still not sure which would work for me, so thought I would ask directly figuring someone, or someones, has probably built something similar.

As an aside I was thinking of having the units flicker on, individually different, when powered up as shop fluorescents do. This is only a interest, getting the lights set up is the priority

thanks,
glenn

Zoot

Use a transistor to drive the LED(s) from Stamp pins if you need very bright LEDs or many of them in a "unit". The Stamp pins can only handle about 20ma, and there are limitations on the total current through all pins (e.g. if you have an LED on every pin, and turn them all on, you may fry your Stamp). You can get packs of cheap NPN transistors at Radio Shack; online for even cheaper.

In the attached schematic, the resistor between the anode of the LED and V+ needs to be matched to the LED -- that's your brightness.

You might also think about hooking up the LED drivers to the Stamp pins taking advantage of the 4-8 pin ports --- e.g. if you hook the LEDs up to pins 4-7, you can use OUTB to change all 4 led units at once (e.g. OUTB = %0110 or OUTB = %0000), rather than LED1 = 0, LED2 = 1, LED3 = 1, LED4 = 1, etc.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
When the going gets weird, the weird turn pro. -- HST

Blackbird455

gchrt,


What kind of stamp are you going to use? 1, or a 2? What kind of leds are you using......Radio shack type? All I have ever done with the stamps is control LED's , while not the most educated stamp user , I do have alot of experience with LED's. Tell me what voltage (vf) and amperage each led has, and I can give you code and schematic to meet your needs.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
ETERNAL NOOB, you could learn alot from a dummy.......

"one should not profess ones ignorance, one should just read more books"
······························································ ......unknown

gchrt

Zoot, thanks for the reply. I was aware of the current restrictions through the stamp itself. knowing I needed some other setup to accomplish my need.
I had seen the transistor setup and considered 2803 arrays with 74HC595's. And thanks for the tip on the OUTB, very useful to know.

Blackbird455, I am using a BS2 and the leds will be white at most likely 3.4 vf at 25mA.
I just ordered 20 RL5-W6030's from SuperBriteLeds.com for a test arrangement with two 595's by themselves to see how this may work, but I am certainly all ears.
I need enough light to fully illuminate the interior and I would prefer that light to come from these four units of 6-8 leds.

allanlane5

If you get low-current LED's, which take like 1 mA to light fully (and they're as bright as normal LED's, so that's not a problem) you don't need any additional hardware.

You then have a choice. Hook the 4 LED's (each with its own 4.7 Kohm current limiting resistor) in parallel to a single pin. One BS2 pin can easily drive 4 mA.

Or you can hook each LED (with current limiting resistor) to its own BS2 I/O pin and get individual LED control.

Jessicat

I have used those from superbright, and they do mean 30 degrees !! RL5-W15120 White LED would have been a better choice, or http://www.luxeonstar.com/item.php?id=5141&link_str=1394&partno=LXML-PWW1-0040 these have a 140 degree angle.

gchrt

Jessicat, thanks for the recommendations. I'm will be putting these behind a slight diffuser and wanted the effect of a line so hopefully that 30 deg will work.