Hi, this is my first semester in college. I have basically no previous knowledge of circuits and I need help bad.

My final project is a simple 24 hour clock and I think I might have bought the wrong type of chip.

My circuit is basically from a 4-bit binary counter chip (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-8246-5-ND)

wired to a BCD to 7-segment decoder chip (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-3712-5-ND)

wired to a 7-segment common cathode display.

I know my counter works and my display works but I have no output coming from my converter chip. I know I have all of the inputs wired correctly and I have tried it with different chips to see if its not just a bad chip but it just doesn't work. Did I buy the wrong part?

If it is the wrong part then hopefully I can either do overnight shipping or I can just make it into a binary clock(I only have to get a 50% to get an A in the class so I can afford a couple points off).

 

Can you post up a schematic? What is that "converter chip"?

 

The "converter" chip is right here(I meant decoder): http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-3712-5-ND

The datasheet is on there to. Its a 7447 chip(specifically a SN74LS47N).

The schematic is below. Please just look at the first two chips on top. The left one is the counter and the right one is the decoder chip. The millions of inverters on the right is just because the only display the program had was a common anode display and I wanted a common cathode. Also, you can ignore all the logic gates in between the counter chip and the decoder chip. I connected the 6 chips together differently than you would regularly connect them because it made more sense to me for some reason. The schematic shown is on a program and the clock works on it(with the exception of the second hour digit but I know how to connect that). Sorry if it looks sloppy and is hard to differ between connections (I think some are overlapped/so close that you cant tell). The program I work on sucks.

Is there any reason why the outputs aren't showing up is because the inputs coming from the counter is too weak? Or does that not matter?

 

Are your IC's connected to Vcc in your schematic? I cannot locate the connection.
Also, can you check if the inputs of the 7447 are correct, through a simulation? If so, we can be sure the problem is with the 7447.

 

The schematic you are looking at is from a program which is able to test your circuit in real-time. It all works in the simulator so I know the connections have to be right.

The big problem is that in order to do the final project, we had to buy everything over the internet with no real directions on what to look for. So I have a huge feeling that there was some type of specification thats making it all off. I know it isn't the soldering on my board btw because I also tested everything separately on a breadboard and the exact same problem showed up.

 

I think it needs a red LED with 300 Ohm resister, maybe two LED's.

 

It's due Thursday? Maybe we could send you the parts by cruise missile.
John

 

Good news. My school ECE store had 8 7447 chips left(which is rare around this time) which are different from the ones I ordered. These should work since I have already used them in a lab earlier this year.So thanks to everyone who posted. I have to study all night tonight for my last final but I have all day and night tomorrow to finish my clock. I will let you all know how everything turns out in the end.

Thanks all,
~David

 

There are quite a few connections in the schematic shown. Did the software auto-route a PCB that you created, or did you assemble it on proto-board or point to point such as wire wrap?

I've rarely had a logic IC "go bad" unless I was aware of it by too much heat, smoke appearing, capacitors exploding, and other subtle signs of connecting the wrong power supply to a circuit.

 

How exactly do you have the displays hooked up to the 7447? Remember - the 7447 has open collector outputs... Also, what's the common of the displays connected to?

Other issues you will run into if you are building this:
- Decoupling capacitors are not shown on the schematic
- Power and ground pins for the jellybean logic ICs are not shown on the schematic
- You have switches that connect outputs to ground.
- When drawing schematics, it is OK to use multiple Vcc or ground symbols to simplify the drawing by getting rid of some of the lines

/mike