ATS25 AMP mistake update

[Alphaacres]

I bought a key with the receiver I expect upgrades.

[slartibartphast]

F8 works fine for me, which is why I was wondering what the issue was.
I looked at the board too but have no idea how to id some of the chips, I am no expert. But I saw a 5v marked hole, but it only measured about 4 volts. So it seems they want to have 5v but it's not working.

I only have some wire for antenna so hard to get much signal so i was surprised it did decode.

[G8PTN]

F8 works fine for me, which is why I was wondering what the issue was.
I looked at the board too but have no idea how to id some of the chips, I am no expert. But I saw a 5v marked hole, but it only measured about 4 volts. So it seems they want to have 5v but it's not working.

Hi,
- 5V
Although the PCB is marked "5V", it is actually the Lithium battery voltage after the ON/OFF switch.
There is no voltage boost circuitry on the ATS25-AMP, unlike the Max Decoder.
A fully charged battery will be around 4.2V, 3.7V typical and 3.0V when close to discharged.

- FT8, CW/RTTY Decoding
My understanding is that the FT8 decoding is done using DSP inside the ESP32. This uses the amplified audio output from the LM/HT386.
For CW/RTTY, the LM/HT567 performs the tone detection, which is then sent to the ESP32 for decoding. I am not sure why the tone detection can’t also be done in DSP, perhaps there is not enough compute power.

As previously stated, the decoder circuitry will work below 5V, but it may not work correctly when the battery voltage reduces.
73, Dave

[slartibartphast]

instead of cutting traces I wonder if just lifting the power pins for both chips and supplying them with 5v from a booster would work.

[G8PTN]

instead of cutting traces I wonder if just lifting the power pins for both chips and supplying them with 5v from a booster would work.

It would be possible to lift the power pins to the ICs, but there is at least one pull-up resistor and also the decoupling capacitors. It’s more likely the SMD’s, or PCB will be damaged trying to lift the pins.

Looking at an image I found elsewhere, I think the power connections to the DIGI decoder ICs and associated components can be isolated with two cuts on the bottom side of the PCB. A strap would be required as shown to reconnect the switched battery voltage to the LDO regulators. A charge pump would then need to be added to power the isolated DIGI decoder section.

Care would need to be taken with any modifications on the bottom side of the PCB since it sits on top of the battery.

There may be other possible modifications, such as replacing the switched battery feed with the output of a medium power 5V boost regulator. This would be quite simple, but means there will be more switching noise, which may cause interference on the radio side.

If your ATS25 AMP is working, I would leave it and recharge the battery as required if there is a problem.
73, Dave

[G8PTN]

An observation on the DIGI decoder circuit is that the low voltage failure in CW/RTTY mode may be due to the voltage levels presented to the ESP32.

The output of the LM567 (Pin 8) is open collector, so the logic high level is set by the resistors. The values are such that the voltage at the ESP32 does not exceed 3.3V with a DIGI decoder supply voltage of 5V.

The logic high level presented to the ESP32 will be approximately 0.49 x 5V = 2.45V.

In the case of the ATS25-AMP, the VCC to the DIGI decoder is Vbatt and so as the battery voltage falls, the VIH requirement on the ESP32 will not be met.

Although the circuit failure may also be due to the low voltage to the LM386 and LM567, I am not sure why the pull-up on the output of the LM567 is not connected to VDD (3.3V) of the ESP32, which would guarantee the correct levels without any risk of the input being over driven (example below).

73, Dave

[Alphaacres]

Could you show us a before and after pictures so I know what to add and remove.

[G8PTN]

Hi,
I have not made this change to my ATS-25 AMP, it was an observation after looking at the circuit diagram of the DIGI decoder.
It may be the case that without increasing the VCC to the LM386 and LM567, the circuit will still not behave correctly.
The change could be simplified without shorting out the 1kΩ resistor.
As stated previously, if your ATS25-AMP is working, I would not make any modifications.
73, Dave

[Alphaacres]

Thank you for an honest answer.

[kou]

Please tell me where the input and output are for the mute circuit of the ats25 series.