CTCSS tone generators. LM566??

[G6Tanuki]

I need to build a cheap-and-cheerful oscillator to produce a tone between 94.5 and 118.8Hz as a replacement for the old 1750Hz repeater access toneburst in a 1970s-era Trio-Kenwood TR-7800.

Back in the 70s the LM/NE566 tone generator was the go-to chip for this sort of thing, it being a bit more stable than a brute-force 555 chip followed by a R:C filter to bludgeon some sort of sinusoidality into the output.

Purists would no doubt suggest a R:C phase-shift oscillator, I built plenty of these for pulsed-tone-testing of SSB transmitters in times-past, but they are hard to tune to a specific frequency, and the capacitors needed for 100Hz or so get big.

The 566 does have the advantage of using only a single variable resistor to tweak the frequency.

Suggestions, please?

[SiriusHardware]

Another possibility in a smallish outline would be something like a PIC or AVR microprocessor generating a stream of PWM sinewave values followed by a little bit of R-C filtering to turn the PWM into analogue audio. I'm not sure what the smallest AVR or PIC (ie, with the least number of pins) with at least one PWM output is.

This approach would have the advantage of making it easy to choose between two or more tones and any tones so generated would be extremely stable.

If literally replacing the toneburst with a CTCSS generator you might have to find a different injection point for the sub-audible tone, PMR radios (which this is not, I know) typically have an 'in-band audio' input for selcall tones etc, and another one which bypasses the audio filtering which would otherwise knock out the relatively low CTCSS tone frequencies on the way to the modulator.

[mickm3for]

Hi see https://www.zl2pd.com/CTCSS_encoder.html i have built and used lots of these uses a attiny85 mcu stores tone in eeprom Mick

[SiriusHardware]

That is is pretty much exactly what I had in mind, I notice the author has even been kind enough to make the hex code available. Easily built on veroboard if needed.

The use of an 8MHz crystal does mean that there will be a 'birdie' from the unit on 144.000MHz whenever the unit is powered, but that is right on the band edge and therefore not likely to be a problem. There will also be sprogs on 432.000MHz and 440.000MHz.

[G6Tanuki]

While the use of a PIC or the Atmel type approach would be the obvious way to go were I to be doing this for a series-production run to be sold commercially, it doesn't seem sane for a one-off, specially as I would have to buy a USB-to-Atmel programmer, whoch would only get used once...

I'm still inclined to try something using the likes of a 566 or the VCO part of a CD4046,and a couple of the multi-turn Trimpots I already have here to set the frequency. Even if it's not totally stable long-term I don't mind having to stick a screwdriver in a hole and give the thing a tweak every few months.

[Chrispy57]

"Suggestions please" ..... XR-2206 ?

Cheers
Chris

[G6Tanuki]

I'd forgotten about them! But definitely on my list of chips-to-investigate! Our friends in Cricklewood seem to stock them stilll.. https://www.cricklewoodelectronics.com/XR2206CP.html

[Chrispy57]

Yes, and I picked up three for £7 inclusive from China a couple of years ago for my Wobbulator project.

Cheers
Chris

[SiriusHardware]

I have heard that the XR2206 is quite widely... not exactly totally faked, but that there are clones of it (labelled as genuine XR2206s) which don't perform exactly like the originals. Unfortunately I can't back this up with documentary evidence, as I can't remember where I saw that.

I'm not suggesting that a reputable seller like Cricklewood would be selling those, but watch out if you source them from anywhere further east.

[G6Tanuki]

Yes, I'm well familiar with fake ICs/transistors [being the sort of person who has a lot of exposure to Motorola MRF-series].

Methinks that Cricklewood are probably selling old-stock; plenty of the ICs I've bought from them in the past [LM380 and TA-series audio-power chips] have been clearly 'old' not newly-made-and-marked-up-in-the-last-few-days somewhere in the East.

[Steve_Bell]

Remember the ICL8038 waveform generator?

[SiriusHardware]

G6Tanuki, I get that you are keen to arrive at an 'analogue' solution for this - however one part of your objection to the idea of using something like the AtTiny was that you would need to make the one-off purchase of a programmer for it.

If you already have an Arduino Uno, as well you might, you already have a programmer for these ICs. You just have to upload a specific sketch to the Uno to turn it into an ISP programmer for the AtTiny. (See info below, found online).

...And now I'll shut up.

Programming the ATtiny85 is a useful skill for creating compact and custom microcontroller-based projects. Here’s a step-by-step guide on how to program it:

Add Support for ATtiny85 in Arduino IDE:
By default, the Arduino IDE doesn’t support the ATtiny85. To add support:
Go to Arduino ? Preferences.
Scroll down to Additional Board Managers URLs.
Add the following URL: 1.
Press OK and restart the Arduino IDE.
Install the ATtiny Board Package:
In the Arduino IDE, go to Tools ? Board ? Boards Manager.
Type attiny in the search bar.
Install the Attiny by David A. Mellis package.
Now you’ll find the ATtiny85 board under Tools ? Board ? Attiny85.

Set Up Arduino Uno in ISP Mode:
We want to program the ATtiny85 from the Arduino IDE, which requires burning the bootloader to the ATtiny85.
Upload the ISP sketch to your Arduino Uno:
In the Arduino IDE, select File ? Examples ? 11. Arduino ISP ? ArduinoISP.
Upload this sketch to your Arduino Uno.

Understand ATtiny85 Pin Labels:
The ATtiny85 has 8 pins, but we’ll focus on 6 of them:
MISO, MOSI, SCK, RESET, Ground, and Positive.
Pin 1 is marked with a dot. The other pins follow an anti-clockwise order around the chip.

Make Connections:
Connect the Arduino Uno and ATtiny85 as follows:
Arduino Uno ? ATtiny85:
5V ? VCC
GND ? GND
Pin 13 (SCK) ? Pin 7 (SCK)
Pin 12 (MISO) ? Pin 6 (MISO)
Pin 11 (MOSI) ? Pin 5 (MOSI)
Pin 10 (RESET) ? Pin 1 (RESET)

Upload Your Program:
Write your program in the Arduino IDE.
Select the ATtiny85 board under Tools ? Board.
Choose the appropriate clock frequency (e.g., 8 MHz internal).
Click Upload to program the ATtiny85.

[G6Tanuki]

Have ordered an XR2206 from Cricklewood, along with a bunch of other stuff like IRF840 power FETs for a little RF amplifier project. It's amazing how much power you can get from such things at a wonderfully low price.

Before this, I spent an interesting hour with Excel looking at the various divide-by-N options available in cheap TTL chips and the frequencies available in ceramic resonators, without coming to any good conclusions.

[PA3DAF, Erwin]

I build a few Arduino based CTCSS generators by PA3GUO. They can be made small enough to fit in a TR7800. I used them in a TR9130, FT480R and FT225RD.

Link: http://www.pa3guo.com/downloads.html

Youtube link of my FT480R with CTCSS https://www.youtube.com/watch?v=jzlpevdDzxA

Erwin, PA3DAF

[Oldmadham]

Back in the day VK6UU was playing around with CTSS encoders & decoders & published a number of simple encoders in the WIA mag "AR". He found the VCO in a 567 was stable enough to use in an encoder.

It was very simple, worked well & appeared all over the 'Net a couple of years ago.
I can't find it anywhere, now!

[Terry_VK5TM]

Pages 46 & 47 AR Mag Jul 1996

Download here https://www.worldradiohistory.com/Au...teur-Radio.htm

[G6Tanuki]

Originally Posted by Terry_VK5TM

Pages 46 & 47 AR Mag Jul 1996

Download here https://www.worldradiohistory.com/Au...teur-Radio.htm

Thanks! It gives me another path to follow if my XR2206 approach doesn't work out.

[dglcomp]

We used picAXE microcontrollers at school, basically a bootstrapped PIC microcontroller designed to be simple to program. I believe all had a sound command that could output to a piezo speaker.
Programming was done with a simple 3 wire RS232 interface and the programming software was a free download.

[G6Tanuki]

Originally Posted by dglcomp

We used picAXE microcontrollers at school, basically a bootstrapped PIC microcontroller designed to be simple to program. I believe all had a sound command that could output to a piezo speaker.
Programming was done with a simple 3 wire RS232 interface and the programming software was a free download.

All the PIC, Arduino and Atmel stuff I've seen sems to involve crystals, the cost of which would alone exceed my target-budget for this particular project.

"Programming" via a 10KOhm Bourns Trimpot from my stash of such bits is more what I had in mind. Having to tweak it occasionally to compensate for component ageing is not a problem.

[Terry_VK5TM]

Forgetting the need for a programmer for the moment - more modern PIC's have their own internal oscillator that is accurate to about 1% and some can be trimmed to better than that, so it would be feasible to do one very cheaply.

As an adjunct to the July AR article - for others that haven't read it - the following month (August) he uses a phase shift oscillator to do CTCSS encoding.