Easy to get confused.

 

Here is the construction of the main part of the board. Still have a few little things to do, then I can begin building the electrical components.

 

Will I need to use the COM for anything on the ULN2803's? What is the purpose of the COM on this chip?

 

From page 10 of the datasheet:

9.4.1 Inductive Load Drive
When the COM pin is tied to the coil supply voltage, ULN2803A is able to drive inductive
loads and suppress the kick-back voltage via the internal free wheeling diodes.

9.4.2 Resistive Load Drive
When driving a resistive load, a pull-up resistor is needed
in order for ULN2803A to sink current and for there
to be a logic high level.
The COM pin can be left floating for these application

So, you won't be using COM. COM goes to the relay supply voltage when driving relays. If you were using this driver the diodes that your placing on the relays would be internal to the ULN parts with COM connected.

 

Okay, thank you.

 

Hello all,
Can I join the conversation with a similar problem / project . I hope thread starter and all the people who have replied don't have any problem.
I need help with selection of parts. Can you all please look at the ckt and let me know ? Does this work with the parts I selected?

 

..........
I need help with selection of parts. Can you all please look at the ckt and let me know ? Does this work with the parts I selected?

The red LED requires 5.1V and the green LED requires 6.6v to turn on so the 6V from your 4 batteries is not sufficient, you need at least 5 batteries.
Also each LED requires a resistor in series to limit the current to the desired value since LEDs are diodes and the current above their turn-on voltage is limited only by the external resistance.
The required resistance is Rled = (Vbat-Vled)/Iled.

The MOSFET type is okay.

Note that your design gives a wrong answer indication (red LED) as soon as a State is selected (is that what you want?).
If you want the red LED to light only when a wrong answer is selected then you need to reverse the City and State connections, and add diodes to the MOSFET source from all the incorrect answers.

 

Thank you for the prompt response.
Yes, I want RED LED to light only when wrong answer is selected. I modified the circuit diagram and calculated current limiting resistor values for Green LED and Red LED.
Please let me know if this change is good enough.

 

Looks good to me.

 

I just noticed that you don't need diodes for the isolated incorrect answers. Those can all be tied together and directly connected to the MOSFET source.
You only need diodes to the correct answer lines.

 

I got it. Thanks a lot.

 

Glad to see others getting some use out of this thread

I have spent the last week or so contructing the quiz cabinet and trying to finalize my PCB layout. I found a pretty decent PCB tool from DesignSpark and have simplified my design as best I can. I do not know if you will be able to open the file without the designspark program but if you can, please let me know how it looks.

So now I have a couple decisions to make. Do I send the file out to have the PCB made or do I try to drill and etch it myself. I have etched a PCB in the past but it was a much simpler design and was all surface mount. This board will have well over 100 holes to be drilled. You can see by the design that I have made one big change from the initial plan. The park decided they wanted closer to 50 selections to choose from! . Thats a far cry from my initial 16. The concept stayed the same, but the volume of components and size of the board obviously got bigger. I just dont know if I cn drill all those holes correctly or not but on the flip side, I don't know how to go about sending a drawing out to be done professionally. Any guidence here would be great. Here is the PCB file and a picture of the cabinet almost complete. Sorry for the bad picture but I had it tucked away before I decided to get a picture. You can see the metal discs down the left side for the selections, and the metal discs inside each box for the answers.

EDIT*** I had to change the ALT_Quiz file to a .txt extention to get it to upload. Just change it back to .PCB to view it.

EDIT 2**** the forum document checksums are smarter than me I can not upload the DesignSpark file as its not a valid format and I can not change the extension as it realizes its not a real picture...lol. So I just did a screen cap.

 

Most PCB houses require Gerber file format. I am not familiar with DesignSpark; can they export to Gerber format? I use DipTrace and Oshpark to make my PCBs. It's as simple as uploading a zip file with the Gerber files and paying!

 

Most PCB houses require Gerber file format. I am not familiar with DesignSpark; can they export to Gerber format? I use DipTrace and Oshpark to make my PCBs. It's as simple as uploading a zip file with the Gerber files and paying!

Yes, DesignSpark does the conversion for you to a .GBR file along with drill files. There are lots of different options, just hoping I have them all correct..

 

Yes, DesignSpark does the conversion for you to a .GBR file along with drill files. There are lots of different options, just hoping I have them all correct..

If you look at the PCB vendor websites they should be able to help you decide among the various options.

 

If you look at the PCB vendor websites they should be able to help you decide among the various options.

Thanks.

Does anyone have any recommendations for a manufacturer? Most seem to only want to do double sided boards and mine is single sided.

 

.................Does anyone have any recommendations for a manufacturer? Most seem to only want to do double sided boards and mine is single sided.

You can do a single-sided board using a double sided process.
There's just no traces on the back side, but there will be through-hole vias so you can solder all the through-hole devices on the back side, which makes the soldering easier.
You can flood the back side with a ground-plane if you like so the vendor doesn't have to strip off all the copper (that makes the vendor happy).

 

So its better to do all my traces on the top layer? For some reason I thought all traces on the bottom would have been easier. Thanks for the heads up!

 

So its better to do all my traces on the top layer? For some reason I thought all traces on the bottom would have been easier. Thanks for the heads up!

Didn't mean to imply that.
You can put the traces on either side of the board, whichever seems more convenient.

 

Hello guys. I have the construction of the board just about done and I have the PCB I designed being delivered by the end of this week. Here is a picture of the final PCB design. I know I could have simplified a little by going with DPDT relays, but I went with SPDT this round instead. I hope this works out okay. The ONLY thing I am not crazy about is if the person attaches the "answer" pen first, the red light will come on until they attach the "question" pen. If they do it like they are supposed to and attach the "question" pen first, it will work fine.