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BCD & Chester's Approach

This discussion was created from comments split from: MPET Advanced Thread.


  • I'm experimenting with a 7 segment display, a 7400 series driver and three rocker switches to count from 000 to 111. Think I need to stick in a few resistors (not shown) before the display LEDs.

  • This is fantastic Chester! Looking forward to you charting your progress. I am splitting this to its own thread so it does not get lost in the shuffle.

  • Looks Great! I have an idea for a 3 ring, 8 position rotary switch to use for channel selection that would fit right into what you are working on.

  • Chester, I heard you chatting with George and Steve about this and I think it is a great idea. I told Chuck that I want to have a visual indicator of what Channel the Ritron is tuned to and your concept would accomplish that.

    I'd also like to have an LCD or LED, a very small one, to display the number. At the meeting last Thursday, when you and I were chatting with Aaron, he had a small display device in the palm of his hand...Chuck is 'consulting' with me today on my project and he and I have already discussed the possibility of incorporating your idea into my project. Permissions and rights will be applied for, of course.

    Thanks for sharing this.

    Take care,


  • edited January 2017

    Paul et al,
    I'm still making choices about which driver chip to use. So far, I think I need the 7447 chip to drive a common annode type LED display. The binary input to the chip is a logical high which is also what CS0, CS1 and CS3 are looking for. I'm going to check this with a couple of OMARC brainiacs for their guru guidance. All this stuff is on Ebay and etc. I thought I had the right junk parts to do this but everything I have is either the wrong thing or electronically fried. I'll be sure to "clue you in" when I know more about what will work.

    7446 BCD to 7 segment decoder/driver with 30V open collector outputs anode
    7447 BCD to 7-segment decoder/driver with 15V open collector outputs anode
    7448 BCD to 7-segment decoder/driver with Internal Pull-ups cathode
    7449 BCD to 7-segment decoder/driver with open collector outputs cathode

    '46 and '47 are for common-anode LEDs, whereas '48 and '49 are for common-cathode LEDs.

    For the common-anode types, '46 allows a higher drive voltage than '47.
    For the common-cathode types, the difference between '48 and '49 is that '48 has

    "ripple-blanking input" (for suppressing leading zeroes), which the '49 has not.

  • edited January 2017

    Download spec sheets for the driver chips at:

  • Here's a snap of my breadboard version with four dead SN7447 chips that all do nothing. RIP. Well, I gave 'em a chance anyway...

  • edited February 2017

    This comment was first posted on January 27.
    It was edited on February 26.
    It was edited again on February 28.

  • to you Chester...I know what a 'breadboard' looks like. I won't embarrass myself further by telling you the mental image I had of what a 'breadboard' is.

    Anyway all this info is helpful and providing the thread most useful.

    Thanks and take care,


  • This is just one way to breadboard. It can be done with "whole through" circuit board as well. So the word "breadboard" is also a verb. To "breadboard" means to build a prototype circuit for testing, development or for proof of concept.

  • I've decided to set the most modest of goals with respect to the Muppet Radio. Doing so has removed a bit of anxiety about this hobby project. My goal now is to just get the thing on the air and communicate over the 805 repeater. Bells and whistles can come later.

    To attain this more modest goal I will use an el Cheapo Baofeng mic and a couple of phono jacks I bought at Radio Shack yesterday. (See below.) Thanks for the source George. It has an 1/8" plug for audio and a 3/32" plug for PTT. This is convenient for connecting the Muppet's "audio" pin 4 and "push to talk pin 14" which switches the radio between listen and transmit. I paid something like six bucks for the mic and the jacks cost another 5. The jacks will also need a wire to "ground" pin 15 (GND). Maybe the mic needs to go to the "power pin" 6, I don't know.

    I've been putting it off but sooner or later I'm going to have to decide exactly where I'm going to drill holes in the plastic box I acquired to put all this stuff in. Once I get everything together I'll lay it out and maybe send you another photo.

  • Thanks Chester and George and all. I am ordering the same Mic and connectors...this info helps me to see how my voice 'GOZINTA' the Microphone which "DUZIT" (turns soon waves into electrical signals) and then "COMZOUTA" the microphone as an electrical signal and then "GOZINTA" the DB-15 Connector to be distributed elsewhere.

    I'm using this project to learn about 'whats under the hood' of a radio and having a great deal of fun. I'm posting some of the parts I'm considering purchasing for the switches on my project...any suggestions or opinions will be welcome.

    Take care all,

  • I love the technical vernacular, Paul! Is it OK for me to use those 3 terms "GOZINTA", "DUZIT" and "COMZOUTA" and give some ideas on the PIN assignment to ensure some peoples MPETs do not go "SMOKEANDBOOMSKI"

    Steve K2GOG

  • You are hereby granted perpetual permission to use my father, Eugene L. Brown's, technical jargon that helped me when I was 8 years old to begin to grasp radio theory.

    My Dad will be happy too.

    Take care,


  • edited February 2017

    You did a great job with your circuit! It is hard to see what you have hooked up or not with the picture.. I saw a couple of things that might be an issue.. One, which I think you pointed out is that the logic is active low. One way you could get around this is to add a hex inverter. This will only give you six inverters (hence the term 'hex" meaning six), but that could be used to flip the logic. The other thing is that it doesn't look like you have the "D" pin grounded (Pin 6). I looked at the state table and it shows that for the lower half of the inputs, 0 - 7, this pin should be low.

    I would be surprised if all of those chips were bad..

    If you get it working, let us know what you did..

    I am using an OLED for my project.. You might have seen it at the meeting, but this is what it will look like.

    I am controlling this OLED with an Arduino. The nice thing about this is that we can use it to show the channel, frequency, call sign if wanted, PL tone, battery level, etc..

    It is truly amazing what technology there is out there and how much things have changed. I would almost never go back to using an old 7 digit display unless I had to.. ;)


  • edited February 2017

    Maybe displaying what number is assigned to each channel is not that important. Just suppose that I had a row of eight momentary switches or buttons, one for each of the eight channels. Imagine that pushing one of those buttons selected a channel and that the button also lit up. That would be enough; Knowing the number of the selected channel is really irrelevant.

    I'm searching the web for a source for eight nice-ish looking momentary buttons that light up when pressed, something like the buttons on a car radio, but illuminated. I could use a voltage divider and an Arduino to convert the button pressed into a signal to control the Muppet's CS0, CS1 and CS2 pins. There are plenty of programs (sketches) floating around in the cyber wilderness that turn one of the Arduino's pins into a volt meter. Eight buttons...eight voltages...eight channels...hmmm...looks like I have a bit of research to do about buttons and Arduino programing.

    Back soon.....

  • Push buttons are readily available and they're cheap. So are LEDs. So, I might just stick some LEDs next to regular buttons if I can't find any buttons with built in lights. Meanwhile I'm back to the Arduino and a few experiments...later gator.

  • Hey, how do you list these posts by date? Comments seem to be getting out of order.

  • Hey Chester, this is really strange. It seems just this one thread's order is all mucked up. I need to brainstorm with Aaron about this.

  • edited February 2017

    My new idea is to use an Arduino to select one of the eight channels. The new design uses momentary push buttons to select one segment of a voltage divider. (Note resistors and button switches in photo below.) The resulting voltage is detected on analog input pin A0 of the Arduino so it knows which button was pushed. In response it lights one of eight corresponding LEDs, and when I figure out the code, it will send a binary number to the muppet's C0, C1 and C2 pins which select the channel the radio operates on. I have yet to figure out how to do that and there are still bugs in my design. But I thought this was as good a time as any to post something about my process. The code I have so far is as follows. Your ideas are welcome and valued...xo

    Routine to read the voltage divider:

    void setup() {
    Serial.begin(9600); // Initialize serial communication.

    void loop() {
    int sensorValue = analogRead(A0); // Read pin A0 for analog number btw 0 & 1023.
    float voltage = sensorValue * (5.0 / 1023.0); // Convert to floating point number btw 0 & 5.

    Serial.println(voltage); // Print out the voltage.



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