Step 6 : Add Some Chips

Again, these are the ones I ordered from Arrow Electronics in February 2006

MC74HC595AN $0.28 ea
DIGITAL HC-SOIC
ON Semiconductor

I now know that SOIC means "Small Outline Integrated Circuit", which implies a surface mount part. The part number listed IS a "PDIP−16", Arrow has the description wrong in their system. I did receive DIP chips. As of 11/05/06 their price is still $0.28.
(Thanks Phil)

E-ULN2803A $0.52 ea
EIGHT DARLINGTON ARRAYS
STMicroelectronics


Be sure to install the IC's in the correct direction! Pin 1 is the square pad in the ExpressPCB image/file.
The IC has a small half circle at the top in the center and pin 1 is the top left pin.
The IC pins are numbered counterclockwise from pin 1.

Step 7 : Power Supply

For most desktop computers, the controller needs a source of 5 volts dc power. This needs to be a regulated source. It could be from your PC, an old PC power supply, a "wall wart", or even batteries.
Many people have had problems with the parallel port signal voltage being low. It may be a good idea to measure the voltage at the port of the computer you plan on using. Your computer will have to be running and you will have to send a "High" signal to the pin to measure this voltage. You can use Vixen with the "Basic Parallel" plugin and the "Test Channels" function to send this "High". Choose the power supply based on this voltage. The 74HC595 can operate on 2-6Vdc. Don't use a power supply that has lower voltage than the port voltage. Compare your pin voltage to the following chart. If your pin voltage is 3.3Vdc you can use a 4.5V supply. My port pin highs measure 4.6 Vdc so my 5.1 Vdc supply should work. I could use up to 6V.



From David Caffey:
"I added two parallel port PCI cards to my PC and the output voltage was too low to correctly trigger the IC's. I lowered the 595 voltage to 4.0 and it worked well." "If you go to Radio Shack and buy the LM317 adjustable voltage regulator, 270 ohm resistor, and a 10K or 20K 10 or 15 turn pot, there is a schematic on the back of the LM317 package that shows you how to build the regulator."

From David Scott:
"I feel the voltage regulator is a must have, and even if you end up not having voltage problems, this will ensure good clean regulated voltage for reliable operation. I have mine hooked up to the 12 volt power from a pc power supply, dropped down to 4 volts. Even if you need the full 5 volts, dropping from 12 to 5 guarantees there will not be any power loss or over loading."

Another suggestion mentioned by Ernie Horning in the forums, add a 4.7K resistor to the parallel port pins 1 & 14. This would be easy to do at the top of the 64 Channel stripboard, just solder one lead of the resistor to the same strip the LPT pin input is connected to and the other lead to the same strip pin 16 of the first 74HC595 is soldered. This is just one possible location. Pick any location that's convenient to Vcc and the inputs.

I got lucky... in one of my Ebay SSR orders the seller added this "extra" item as a thank you.

Step 8 : Testing

For testing I breadboarded sixteen LED's and used Vixen to see what would happen. First I connected channels 1-16, then 17-32, 33-48, 49-64.
Then I went back and connected 1-8 with 17-24, then 1-8 with 25-32, 1-8 with 33-40 , etc, etc.
Next was 9-16 with 17-24, then with 25-32, ... I hope you get the picture... I wish I had 64 leds and a couple more breadboards.
With each test I stepped through "on - off" for each channel and then "all on" and "all off".
The only strange thing I noticed was when the stripboard was powered up and NOT connected to the computer. As I would move my hand over the stripboard random LED's would come on or blink. Very sensitive indeed. Decoupling capacitors it will be.

Step 9 : Bottom Line

1. 1 ea Stripboard           $1.95


2. 8 ea 16 pin Sockets    $0.58


3. 8 ea 18 pin Sockets    $0.55


4. 8 ea 74HC595           $2.24


5. 8 ea ULN2803          $4.16 

Subtotal:              
           
    $9.48



Shipping  is very hard to figure, I bought much more than this
with my orders. When averaged across the orders the cost of this
controller was still less than $13.00

Step 10 : 8 Channel 595 with SSR's. Added 11/15/06

On this 8 channel board with onboard SSR's the 74HC595 and MOC3023 opto's have the same power supply, which in my case is a regulated 5.1 vdc supply. No ULN2803 is needed.

There has been a lot of debate of the input resistor value for the MOC3023 OPTOISOLATOR. Here are my thoughts.

When I built the board I didn't know what I was going to use as a power supply. I planned on 5Vdc +/- 10% tolerance (4.5v -5.5v)
I knew the resistors would have a 5% tolerance.

This is from the Fairchild MOC3023 data sheet:
"3. All devices are guaranteed to trigger at an IF value less than or equal to max IFT. Therefore, recommended operating IF lies between max IFT (30 mA for MOC3020M, 15 mA for MOC3010M and MOC3021M, 10 mA for MOC3011M and MOC3022M, 5 mA for MOC3012M and MOC3023M) and absolute max IF (60 mA)."
And,
Input Forward Voltage: Typical = 1.15V, Max = 1.5V

So... my worst case math:

4.5v - 1.5v = 3v
3v/.005 = 600ohms

I chose 560 ohm.
560 + 5% = 588
560 - 5% = 532
3v/588 = .005102 (The Opto's would be "guaranteed" to trigger.)

Now for the other end of the spectrum:
5.5v - 1.15v = 4.35v
4.35v/532ohm = .00818
.00818 x 8 = .06544 (65.4mA)
If all 8 outputs of the 595 were on at the same time it's still under the 75mA Max VCC limit. So no ULN2803 is needed. If you use a power supply of a different voltage you will have to do your own math, your resistors may have to be a different value.



Daisy chaining the boards shouldn't be a problem, I used screw terminals with a .200" pin pitch from Radio Shack. You can see them in the pic. Just connect Gnd - Gnd, +5v - +5v, STR - STR, CLK - CLK, and SER DATA OUT to DATA IN on the next board.