Need some simple circuitry help with K8055 board

[w3rra]

I am a complete newbie to electronics and light control, and I will hopefully be getting the Velleman K8055 board for Christmas.

I am hoping to interface it with Vixen, but before I can connect any lights I need some basic circuitry help, could someone perhaps please tell me how to connect a simple LED to the board, perhaps powered with 9V if possible?

Look at my complex (yeah, right) circuitry diagram below:



Would this work at all or would it just blow up the board/my PC?
If I'm wiring everything completely wrong could someone please put me in the right direction?

Thanks,
Luke.

[Sharkey]

9V would defiantly blow up the LED. That's for sure.
I never knew how that stuff worked, but I wouldn't try it util you get someone's professional answer.

[w3rra]

If I used a lower voltage battery/more LEDs I wonder if it would work?

[dirknerkle]

The problem is that the normal digital outputs are too low to fire anything. They're less than 1 volt.

Here's a picture of where you can tap enough voltage to trigger something: connect to the front (left side) of the resistors in front of the output LEDS.

Only problem is that the tap is +5vdc and to make it work with normal SSRs, you need to connect the output from there to a ULN2803A to invert the signal, which then goes to the SSRs.

I built a 32-channel controller out of four K8055's and it was slick -- but you either had to redesign the SSRs so that +5v was switched or run the output through a ULN2803A to invert the signal so that the ULN's outputs were ground and +5v was supplied normally to pin1 of typical DIYC ssrs.

I'll see if I can dig up an old circuitboard for a ULN2803a converter for you... Found it. I've attached an ExpressPCB layout file for a 32-channel ULN board that allows taking either a standard parallel port or the K8055 tap as an input and the outputs work with standard DIYC ssrs. I'll put it in the File Library as well -- maybe others might like to have it.

[w3rra]

Ah right, thanks for posting the picture.
I think I understand - does this mean my idea on the circuitry diagram would not work?

Luke

[dirknerkle]

Ah right, thanks for posting the picture.
I think I understand - does this mean my idea on the circuitry diagram would not work?

Luke

Yes, the circuit you made would zap the LED in a New York minute. An LED typically can handle about 1.5-3 volts and usually not more than about 50ma of current (lots of flexibility here, different LEDs can handle more, etc...).

Oh sure, you can connect an LED to a 9v battery straight away, and it'll be REALLY BRIGHT. Then in a second or two it'll get very hot, may start to smell, and it will burn out. You could connect it to 9v if you put about a 1K ohm resistor in line with it, which would take the current down quite a bit and the LED would likely last.

I posted four circuitboards in the COPPER section of the File Library, called ULN2803 Converter (or something like that... duhhhh.... my memory is really getting bad...)

[w3rra]

Ah thanks that's all I needed to know about the board - I'm sure your converter link will come in handy, I really appriciate your helpfulness.

I do have another question, although I will not use a 9V battery, just out of curiosity if I did use 9V or over would it damage the board or my PC? Or is the voltage somehow isolated from the PC?

[Sky-Lights]

Can I ask what kind of fetish do you have for using 9 volt batteries I wonder :lol: ?

If you go to this page :
http://www.velleman.eu/distributor/products/view/?country=be&lang=en&id=351346

it will clearly tell you the boards specs

[w3rra]

Haha, I recently found loads of 9Vs that had collected in the back of my drawer - thought I'd try and find a use for them :)
Thanks for the link, but it does not answer my question - could the board damage my PC if a too high voltage is used? Sorry to sound forceful here but I really am quite a newbie to electronics.

[dirknerkle]

No, no problem with the pc. The K8055 is plugged into an USB port and gets its 5vdc power from the port. Connecting anything on the other end isn't going to flow back to the computer without going through the K8055, and that's designed to protect the PC "just in case."

[w3rra]

That's great dirknerkle, just what I needed to know. Thanks for helping me out here :)

[P. Short]

Dirk,

The K8055 schematic that I found on the web already shows a ULN2803 between the PIC and the digital outputs, so it should be capable of driving an LED or SSR. The diagram that the OP shows is not correct, though. The negative side of the battery should go to the pin labelled GND and the positive side should go to a current limit resistor. The other side of the current limit resistor should go to the LED anode, and the LED cathode should go to a digital output. Alternatively, he could tap off the on-board 5V and forget about the external battery.

[dirknerkle]

Dirk,
The K8055 schematic that I found on the web already shows a ULN2803 between the PIC and the digital outputs, so it should be capable of driving an LED or SSR. ... Alternatively, he could tap off the on-board 5V and forget about the external battery.

Thanks, Phil. I know. The K8055 is an interesting board. I played with it several months before I found DIYC, and I was experimenting with ways to make a K8055 work. It was my first foray back into home-built electronics in about 40 years, and it was great fun. But I found it was a lot easier to loop a piece of cat5 under the front end of the resistor and just tap it with a spot of solder than to try to work on the underside of the board where the solder pads were so tiny and close. Going off the top of the board and using +v also matched the polarity of the parallel port outputs, too.

Then I reengineered Sean Bowf's SSR design so that + and gnd were reversed, and built six custom SSRs for a 48-channel controller (four K8055 boards & 2 LPT ports). At the time it seemed easier to do, and I had never dreamed how my life was about to change... after finding DIYC.

It wasn't until I got further down the road with DIYC that I gained a better understanding for the SSR and controller designs and the logic behind them and they ways they were matched -- a sort of "standard" that I never knew existed. That's when I decided the ULN2803A was a better way to go, and I made the ULN converters to convert both the parallel ports and the K8055 "taps" to be consistent with common DIYC SSRs. It was a long way around to get there -- at my age, I guess I learn more slowly than I used to...:rolleyes:

Soldering taps to the bottom of the K8055 board works well if you have quite excellent soldering skills, and then you can use normal SSRs directly. But it's pretty tricky under there and would be very easy to make a mistake. Soldering off the resistor leads is a slam-dunk to visualize and do or un-do. Were I to really do it again with the K8055 I'd do it entirely differently.

Oh, the things we learn...;-)

[P. Short]

I'm missing something here...why are you soldering cables to the board instead of using the terminal blocks? Bear in mind that I'm just looking at the on-line pdf manual for the board, rather than having a board in my hands.

[dirknerkle]

I'm missing something here...why are you soldering cables to the board instead of using the terminal blocks? Bear in mind that I'm just looking at the on-line pdf manual for the board, rather than having a board in my hands.

I tried that first. The terminal blocks don't deliver enough voltage to do much of anything: about .6 to .8v.

[P. Short]

Dirk,

It isn't the 0.6V to 0.8V that matters, it's the difference between that voltage and the output of the 9V battery (in the setup described in message 5 above) that matters. While I haven't looked at that .pcb file that you provided, I'm pretty sure that it is simply a second copy of the logic that is already present on the K8055 board.

[dirknerkle]

Dirk,

It isn't the 0.6V to 0.8V that matters, it's the difference between that voltage and the output of the 9V battery (in the setup described in message 5 above) that matters. While I haven't looked at that .pcb file that you provided, I'm pretty sure that it is simply a second copy of the logic that is already present on the K8055 board.

Phil, I think you're right. I'm looking at the board now, and I see that the outputs from the onboard PIC trace to the leading side of the resistors, so that explains why that's +4.x volts. The same trace passes through the inputs on the ULN, and the outputs of the ULN do indeed trace to the terminal blocks. However, that sure doesn't explain why the voltage at the terminal blocks is so darned low -- it won't fire an SSR as I've tried it. From what I remember, that output is between .6-.8v.

EDIT: I have the board in front of me and am testing the output voltages at the terminal blocks: .547vdc when measured across the channel terminal and the GND terminal. I have four of these boards and they all measure within .06v of one another at the same places.

[P. Short]

The outputs of the ULN2803 can only sink current, not source it...so you will never see a positive voltage on the output terminal unless something else is pulling it high.

It should be able to fire the DIY SSR boards...you just need to jumper the +5V on the K8055 board to the Clamp pin, and connect the Clamp terminal to pin 1 on the RJ45 on the SSR boards (or find some other way to provide +5V (wrt to ground) to pin 1 on the SSR). You would need to do a similar thing if you are using a commercial SSR...connect the Clamp terminal to the '+' terminal on the commercial SSR, and the digital output terminal to the '-' terminal on the SSR.

[dirknerkle]

I'll try to check it out...


Edit... oop, gonna have to wait... hospital called about my 86yr old mother...