Wiring a small bulb to PLC

Hi guys, have a quick question. I'm working on an AB Micrologix 1500 PLC for class and for my project, one part of it is to hook up a light source and using the PLC, control its intensity.

I was thinking of using a light bulb and then change the voltage going into it. I tried a LED but there were two problems: 1. Not bright enough. 2. Can't dim it?

The question for you guys is, do you guys have any recommendations on bulbs? Something from like home depot and around the diameter of a pencil. The thing that quickly caught my eye was one of those light bulbs from a small maglite flashlight. The problem is hooking it up.

There are 2 legs, (One to ground and one to voltage input)? The flashlight uses 2 AA 1.5V batteries. Should I use a resistor if I want to hook it up to the 5V output?

Thanks,
Kermy

I would reccomend that you use a low wattage incendesent bulb for this purpose.

If your AB PLC has an aux power supply (12, or 24vdc) you may use that power supply. However make sure the bulb will not be too big for the power supply. Watts = Volts x Amps. So if the power supply is 24vdc and the amps is 1.5 amp. make sure your bulb is rated at 24 volts and to be safe 30 watts. You could also use a simple battery.

Next you need to goto Radio Shack and buy a bread-board and some resistors, a small light bulb and base. You will wire a resistor to each output of your plc to be in parrell with the other resistors. As you turn on more outputs on the PLC the light bulb will bet brighter.

You will have to do a little math for this to figure out the wattage of the resistors, and the output wattage of the resistor array to determine the brightness of your bulb.

I'm assuming your PLC has contact outputs. Your wiring should be someting like this.

+------------------< + 12 or 24 volts ->------------------+

|      PLC                                                |

|     out 1       R 1                                     |

+-----||------/\/\/\/\/\----------+-----------(light)-----+

|     out 2       R 2             |

+-----||------/\/\/\/\/\----------+

|     out 3       R 3             |

+-----||------/\/\/\/\/\----------+

|     out 4      R 4              |

+-----||------/\/\/\/\/\----------+

|     out 5      R 5              |

+-----||------/\/\/\/\/\----------+

Have Fun,

Mike

The ML1500 has onboard PWM (Pulse Width Modulation) functionality.

Use it to drive an array of LEDs. The pulse rate must be faster than 50 Hz so that the eye cannot see the individual pulses.

Note: You can only use PWM with transistor outputs, not relay outputs.

If you decide to go with the technique presented by elevmike, also google on "r2r" for a commonly used digital-to-analog circuit.

Does this need to be stepless dimming capability?

Mtn_Bkng_Dave said:

Does this need to be stepless dimming capability?

Click to expand...

I hope not. If so my example dosnt apply.

Mike

elevmike said:

I hope not. If so my example dosnt apply.

Mike

Click to expand...

Not exactly Mike. Your example could very well be configured as a 5 bit A/D converter with the proper choice in resistor values. All analog is stepped, some finer than others. Thats why we have the choice of 12 or 16 bit analog. I suppose I posed the question the wrong way. Perhaps it should have read "How fine do the adjustments in intensity have to be?"

Dave

Sorry, this sounds simple

OK, you want to control a light? Perhaps an LED, or 12V lamp, or a 120V lamp. Goodness, you have a 1500 at your disposal? Nice unit. As far as I know they all have 2 PWM outputs (O:0/2 & O:0/3). Unfortunately these outputs require a minimum of 10mA & have a maximum of 100mA. So, you'll need a transitor to drive your very low voltage bulbs and probably an SSR or SCR to cotrol your AC high voltage bulbs. But, you can control the intensity by setting a fixed frequency and sweeping the pulse width. Yes, all incandescent bulbs are truly DC -- it's the wattage to voltage stuff that'll cause you trouble with direct drive from the PLC.

Light Bulb

Hobby Stores, model trains have small lights called peanut lites,grain of wheat lights, works with twelve volts, have two wires for easy connection.

harriszoom

Ronboom said...

"Yes, all incandescent bulbs are truly DC"

Are you sure you want to say that, ronboom?

Why not? The filaments are not polarity sensitive and they will work with DC. The filament itself is comparable to a resistor made of tungsten. It gives off heat in the form of light. Could you please help me understand why this wouldn't be true?

thx,
ron

If you can find a bulb like hariszoom mentioned above, and it requires <100mA at nominal supply voltage, you can use a program like this one. If you want to make it sweep automatically I have one for that as well.