TM 808 White's

[Skippy]

Regarding that scope input attenuator: If you want to get it "perfect", the 1k0 should be changed to a 1k2 in parallel with a 15k. This will give the correct 1.11111k value; but 1k1 is just in error by 1%, so it's close enough.

[Skippy]

"Do you know someone who has built the tm808 ?"
I know almost nothing about the 808. I contributed to the thread because I had some workable ideas about the unobtainable crystal problem, and I thought it would be good if you included them in a new PCB layout. Then others don't have to mess about making "daughter boards", or programming PIC micro's or MEMS devices to generate the clock waveforms.
My only interest in two-box machines involved making a two-box add-on for my Fisher F75. This has very good non-motion mode performance, so it should be a good match for a two-box. But I also thought a very large ( 60cm ) DD coil would also work equally well.
Lack of time, and too many other projects means it could be ages before I do anything on this.

[berreizeta]

Thx Skippy, I will do.

Do you know someone who has built the tm808 and it works well?

The more I learn, the more doubts I have...

[Skippy]

Change the 1k0 resistor to 1k1, you will get better accuracy on the x100 range ( and a little bit better on the x10 range, too. )

[berreizeta]

Probes for Visual Analyzer -> PC Sound In

[berreizeta]

Visual Analyzer + Windows 10

Oscilloscope, Spectrum Analyzer, etc ... perfect for tuning coils.

https://www.sillanumsoft.org/

[berreizeta]

I have tried with the oscillator of the 4060 and I have not gotten a stable frequency .....

I have ordered the 25600 Hz crystal and I will wait to receive for connect one to the 4024, which I think is the best option.

Adapting the coils to 6400 Hz is not difficult

[Skippy]

"CD4060 does not have Q0, Q1, Q2 and Q10."
Correct, and this is not a problem. If you use the 6.7xxx MHz crystal, you take the Q7 output and connect to the CD4024 input. We are trying to generate ( ideally ) 26600 Hz. This gets divided down by 4 to drive the TX circuit, and divided further to drive ( non-critical ) audio stages, and to synchronise the smpsu oscillator. If you use the 420 / 429kHz ceramic resonator with the CD4060, you use the Q4 output, and connect it to the CD4024 input.
Furthermore: you can change which CD4024 outputs you use. The outputs used are Q2, Q4, Q5, Q6 . These could be changed to Q3, Q5, Q6, Q7, and you input 53200 Hz to the IC. This gives you options with you additional divider / oscillator. You can also use outputs Q1, Q3, Q4, Q5, and input 13300 Hz to the divider. These options may be useful, they may not, but they exist.

[berreizeta]

CD4060 does not have Q0, Q1, Q2 and Q10.

For 52740Hz (26370x2) = 1042300 ohms and 22nF in Q3 = 6592,5Hz

I'll try now....

[Skippy]

Also, your oscillator module design is not going to work. If you power it from a low voltage, like 3V3 etc, its output will be low voltage ( 3V3 / 0V ), which can't be simply connected to another logic IC powered from , say 12V, because both 3V3 and 0V will both be seen as "zero Volts" .
Taking a quick scan over the thread, it looks like the power rail is +/- 8V or +/- 7.5V , in which case the CD4060 should be OK with a 6.7MHz crystal.

[Skippy]

I can't actually see on the schematic what the power supply rail is for the CD4024 etc ... is it 10V or 12V ? I see it's split with a virtual ground generator to +/-5V or 6V for the opamps.

[Skippy]

In case you were unaware of it, there is a 4000-series IC that combines an inverter-based oscillator and a binary divider / ripple-counter, the CD4060. This can be used as a crystal oscillator ( or an R-C based one ), and just use the appropriate divided output .
It would be OK to do the ceramic resonator oscillator, but I think 6.7MHz is too hot for 5V operation. So the better choice is the much faster HC version, the 74HC4060, restricted to 3V to 6V supply rails, though.

[Skippy]

The only common quartz crystal frequency that divides down to nearly the right frequency is 6.7458 MHz, which divided by 256 gives 26351Hz / ( and 6588 Hz operating f ). It's used in some 433 MHz ISM band RF transmitters, and is readily available cheap.
But whether 6.7MHz is a bit 'hot' for 4000 series operating at a low voltage, I can't say. There's always 74HC.. equivalents.

[berreizeta]

[berreizeta]

I have been playing with an active crystal of 1.8432 Mhz (the lowest I have) and a 4060.

On pin14 (Q8*/256) it gives 7200Hz, and stays nailed for ever!.

As I can't find any 6600Hz multiplier I think I'll try the 25.6Khz (= 6400Hz), and adjust the coils to that frequency.