Step 0 : Why?


For those of you who thought the only way to dim with the 595 or Grinch is with a Renard, and that the Hill 320 will Never do Dimming. “MEET my little friend.” I call:

THE BRUTE FORCE DIMMER.

I personally like The Hill320 dimming or not. It gives me almost total control over my whole display. With 320 channels at my disposal I have a couple to spare. Each RJ45 of my Hill320 can control 7 channels. So I was thinking, how about a 7 bit (8bit, 6, 5, 4, 3bit) dimmer? With 7 bits I could get 127 dimming steps. That is a 7 to 1 trade off a sacrifice that I can do with ease. I am not a one to code or to play with PICs or even own a programmer. I thought, “Are there not devices to dim lights already?” I swear I saw one in my kitchen. Yup, you got it, no messing around with zero crossing, no PICs just good OL’ relays transistors and resistors all available at your local Radio Shack and Lowes.
Hee hee. NO shipping! Heck you probably have most of the parts laying around. Now don’t go ripping the dimmer out of the wall. Your wife / mother might get upset.

Step 0 : The Priciple

A household dimmer is made to dim up to 600 Watts. So let’s use it for Christmas lights. If you disassemble a dimmer ($5) the largest component is the potentiometer. It is connected in two places at its terminals to the rest of the circuit is in free form floating around it. What I propose is that we replace the pot with a series of fix valued resistors or potentiometers that are triggered by relays that will gradually increase in value such that when they triggered in a binary fashion they appear to dim or brighten. The relays will be triggered by a transistor which in turn is triggered by an input signal from your controller (hill320, 595, Grinch).
The dimmer circuit is isolated from your controller by the relay so, optoisolators are not necessary (you can use them if you want but it would be redundant). The controller output won’t be overloaded because you will only need enough current to trigger a transistor. So all is safe as long as you isolate the rest of the dimmer and do not let it touch anything it could fry with 120V AC.

Step 0 : The Math

Simple stuff, First decide how many bit dimmer you what to build, as in my case 7 bits. Next plug in the dimmer with lights attached. Turn the pot until your lights pop on then turn back just to the point where the light turn off then --do not touch the pot--. Disconnect the dimmer from the AC and the lights. Disconnect the pot from one side of the circuit and measure the resistance from the center terminal to the terminal that is or/was connected to the dimmer circuit. THIS will be your minimal resistance. Mine measured 224K Ohms out of the total scale of 320K Ohms. Now to figure your resistor values per bit step. If you have 7bits you can have 127 levels of brightness so… You can divide your Ohms by your levels to get the lowest bit value then multiply by two for the other 6 bits.
Yuck. OR take your Ohms (224K) divide by 2 and that is your 7th bit(112K) then divide six more times one per bit(56K,28K,14K,7K,3.5(4)K, and2K).
Be sure to find your Minimum Resistance and do your own scale for it may be different

Step 1 : The Stuff

The STUFF:
1- 600 Watt standard light dimmer -$5 @ Lowes, Home Depot, DIY, Walmart
7-5 Volt SPDT relay @ Radio Shack -$3 each, All Electronics Corp - $0.85 ea for 10
7-NPN or PNP transistors @ Radio Shack $2.22 (NPN for the Hill 320 and PNP for the 595 or Grinch)
7-1000Ohm resistors (1KOhm)
7- General purpose diodes (1N914)
1- Standard ac outlet
1- PC AC supply cord or any grounded cord
1- Copper clad perf board @ Radio Shack
3- 10K Pots
3- 100K Pots
1-500K Pot These Pots are to adjust your dimming levels to those you calculated. Use whatever you deem appropriate. I used fixed resistors. Because they are what I had lying around. i do not suggest this because they make the steps of dimming appear too flickery r/t the resistance varience of fixed reisitors. USE POTS!

Step 2 : The Hill320 DIMMER Schematic