Hello all,

I've been working on an LED circuit that will act like radio buttons... when a momentary switch is pressed it latches it's LED and disconnects any previously latched/lit LED. The circuit is capable of triggering 8 LEDs but my application only requires 4. Here's what I've come up with from a schematic that was provided in another forum. I've done a parts layout on perfboard. Being the hobbiest that I am, it would be great to have another set of eyes check my work.

 

WOW, what a nice schematic !

The switches go directly to the U1 inputs, not through the resistors.

C2 should be as close as possible to the U1 power and GND pins, with the shortest possible leads.

ak

 

WOW, what a nice schematic !

The switches go directly to the U1 inputs, not through the resistors.

C2 should be as close as possible to the U1 power and GND pins, with the shortest possible leads.

ak

Thanks. I looked at the RN at least 50 times and it never dawned on me that they weren't in series with the switches.

 

Here's an updated drawing. I believe I fixed the issue with the RN and I relocated C2 closer to pins 1 & 20.

 

C2 still needs work. Look at the path length of the connection from U1 pin 10 to C2.

The best way is to put on the bottom side of the board in a straight line between pins 10 and 20.

ak

 

You mean pins 10 and 1?

 

Pin 1 needs to be connected to GND, but it is a signal pin, not a power pin. Pin 20 is Vdd, the CMOS equivalent of Vcc in the bipolar world. Decoupling is required between all power pins and the chip's ground pin(s).

ak

 

The latest... I also cleaned up the long jumper paths from pins 10 and 11. I also updated the board to the dotted type I'll be using instead of a bussed breadboard. I'm really excited to build this version!

While we have the discussion going, can you help me understand the function of C3? With it connected only to GND, I'm struggling to grasp its purpose.

 

If this is a two-sided circuit board then you could possibly make the layout work. But presently the common lead from all of the resistors crosses all of the input traces and is a massive short circuit. And C2 under the IC can not be built that way. Put it at one end or the other. AND te angled runners pass far to cxlose to the solder pads to be reliably produced.
Does your layout software allow having a trace pass between IC solder pads? That would be very useful.

 

If this is a two-sided circuit board then you could possibly make the layout work. But presently the common lead from all of the resistors crosses all of the input traces and is a massive short circuit. And C2 under the IC can not be built that way. Put it at one end or the other. AND te angled runners pass far to cxlose to the solder pads to be reliably produced.
Does your layout software allow having a trace pass between IC solder pads? That would be very useful.

It's a prototyping board with jumpers. No traces involved. The common lead you mentioned will be on the back of the board and angled jumpers on top will connect the switches to Rs and U1 pins. C2 also on the back side.
I'm feeling a little sad that you thought I was that clueless.

 

It looks like a circuit board layout study, such as I have done quite a few times. That is why I asked about the artwork program. Certainly I did not intend to be rude at all.
In addition, this section DOES get quite a few postings from folks who really ARE clueless. The circuit is quite good, I had not seen one done that way before. And asking questions is a good way to learn. I learned not to ask if it is a PCB layout unless the TS tells us it is.

 

Certainly I did not intend to be rude at all.

Oh, no problem. It's all good. I was being light-hearted about it. Sorry if I came off snippy.

 

Thanks for this circuit!

I was looking for a radio button switch for a remote antenna switch application for a ham radio project.

I'll need to add output transistors to apply voltage to control lines to remote antenna switch.