Looking for off-the-shelf display to use in a PIC project

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Bob D.

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Can anyone recommend a display for my next project? I want to build a frequency display for my old Heathkit HW-101. I have a TTL signal derived from the VFO available out of the spare jack on the back of the rig. This will basically be a frequency counter with an offset to show where the rig is tuned. I need 7 digits with decimal points to separate the MHz, KHz, and Hz (i.e. 14.347.00). There is no other information to display. The size of the display isn't important.

Bob D.
 
Can't recommend any in particular (I build my own), but perhaps have a search for PLJ-8LED-H RF Signal Frequency Counter on Ebay etc.
Does have one digit more than you want and I believe it can do IF offsets etc and they are not expensive.
 
Sounds like you just need a standard 16x1 display using the HD44780 chip. Very cheap and lots of example code available. If you use 4 bit mode then it only needs 7 or 8 I/O pins.

Mike.
 
Pommie said:
Sounds like you just need a standard 16x1 display using the HD44780 chip. Very cheap and lots of example code available. If you use 4 bit mode then it only needs 7 or 8 I/O pins.

Mike.
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I would suggest a two line display - you can always find some thing to put on a second line

Two line displays are probably easier to source, and likely to be cheaper?.

The entire project is easily developed from the antique MicroChip application note for a frequency counter - or better still the (still very old) modified versions using an LCD display (simple job to add an IF offset.). However, a lot of the new enhanced peripherals would make it even easier than the clever way they did it back then.
 
A MAX7219 LED display might do the job nicely. These displays essentially use a SPI interface (clock, data and /CS), and the MAX7219 does the number-to-segments for you.

Pommie's solution and mine require a microcontroller to interface between the TTL output and the display (i.e., the displays aren't frequency counters).
 


The MAX7219 LED display sounds like just what I need. Looks like the MAX7219 chip saves a lot of I/O pins and code!
 
Yep, they are fairly straight forward to use and handle all the multiplexing internally, saving your code from needing to do the busy work of keeping the display going. If you want to build your own, a couple 4-digit multiplexed modules really simplify board layout. Hard to beat the 8-digif ebay nodules for a few bucks!
 
Reactions: jjw
Yes, they are silly money - I'm currently sat next to two of those modules in series, as I'm displaying four lots of four digits. If you buy the MAX7219 chips from RS Components they cost many times more than the Chinese modules do, as we're using them to feed much larger (1 inch) 7 segment LED's.

I ordered another 10 of the Chinese modules the other day, and they are less than £1 apiece - crazy.

If I was going to be REALLY picky, with the two modules one is 'slightly' brighter than the other, perhaps different batches? - it shouldn't be voltage drop, as they use constant current.
 
Nigel Goodwin said:
If I was going to be REALLY picky, with the two modules one is 'slightly' brighter than the other, perhaps different batches? - it shouldn't be voltage drop, as they use constant current.
Click to expand...

One down-side of the MAX7219 is that there is no individual digit control of brightness of individual digits, just 16 steps of overall brightness. This could be a problem if using different color digits in the same display.

To current is set by a single resistor for all digits. You could swap the resistors to match the brightness of different displays but it would be a trial and error process. The resistors on the Chinese displays are probably under the digits....
 
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Seeing as you said that, I checked - the resistor is nice and accessible on the back (as are all - of the very few - components) - both are 10K.

I've no problem over the slight brightness variation, as I'm only experimenting at the moment.
 
The little 0.91" (128x32), 0.96" (128x64), and 1.3" (128x64) OLED modules use a two pin I2C interface and look pretty nice with a 10x14 font (10 characters per line). The photo below is a 0.96" display...

Good luck on your project.

Cheerful regards, Mike

 
On a related note... I came across an interesting 32-bit counter chip awhile back that I believe would make a nice 100-MHz frequency counter. I ordered a couple of the chips and came up with a design that I thought could perhaps support multiple display types but I have not had a chance to try anything yet. BTW, you should be able to add a 2nd or 3rd counter chip in a design (using a bigger PIC) which would allow you to measure BFO and Mixer frequencies, too.

Cheerful regards, Mike
 
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Mike - K8LH said:
BTW, I really like what this chap did with a little 1.8" TFT display (~$5);
Click to expand...

Yes, great little displays - and various analogue meter versions come in the examples with the library.

What I would say, is to ensure a fast device to feed them - a normal Arduino Uno works but is a bit sluggish (as are low end PIC's), but using fast processors (STM32, ESP32 etc.) really makes them nice and sprightly

Love the VFO display though
 
Look at Nextion Displays. Using UART and can be used stand alone. Very easy to implement into any project

Jason
 
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