Lowe HF-225 antenna and keypad

[WaveyDipole]

Some time ago I acquired a Lowe HF-225 shortwave radio and have recently got around to having a good look at it. There are no signs of bulging capacitors but I did notice that the whip antenna board had been removed. Of course its possible that the input FET had failed or something, but might there had been a performance related reason (interferance with long-wire or co-ax feed antennas) for removing this?

I am also trying to create a keypad emulator using an Arduino. I have come across this reference for building the interface circuit. The output stage is almost identical to the one shown in the manual, except for the resistor feeding Q2. I haver built the circuit on a breadboard using 2N3904 transistors instead of BC547 as that's what I have available. I also omitted the regulator and C1 because I am powering the Arduino via USB at present, although it may need to be included later.

The circuit seems to work - I see pulses from the expected pin on the Arduino pin and via R4 to Q2(b). There are pulses out of Q1(c). There is a voltage of around 10V from the receiver on P and when a character is sent, the voltage at P is being modulated with 3V pulses approximately. So far so good, except it doesn't work. Nothing is happening on the receiver.

I imagine that the output from the Arduino must be held high so as to keep Q2 turned on, which in turn keeps Q1(b) at ground, turning it off and allowing full potential from P. Pulling down the Arduino pin for a the required interval turns off Q2, which turns on Q1 thereby pulling down the voltage at P creating a pulse. That seems to harmonise with the first screenshots in the article but not the second which seems inverted. There is also a long pause after the last pulse which is not mentioned in the protocol description so I am still unsure whether I am generating the pulses correctly, although my oscilloscope trace closely matches the first screenshot. I was hoping that someone might have some notes or information on driving the keyboard input? If so, then it would be appreciated.

I have already written a Python program for the PC to drive the Arduino and was thinking of using an spare ESP32-C3 that I have lying around for this project. I was also thinking of connecting over WiFi or BlueTooth, but as a first step I need to get the Arduino driver working, not to mention getting the antenna sorted before winter.

If anyone can help with any keypad data other than what can be found in the Keypad and HF-225 manuals then it would be appreciated. Unfortunately, although there is a circuit diagram for the keypad circuit, there is no graphic to show the generated waveform.

BTW, there is a large disc battery (presuming Lithium coin type?) on the right hand (rotary control) side. What is this battery used for? Memory backup perhaps? I see there is a separate battery pack connector.

[RogerEvans]

Surely the output pulse P should come from the bottom of R1 and then it would switch from a high of 5V from the regulator to a low of around 0.2V. Also the input and output of the regulator look the wrong way around.

Am I missing something?

Roger

[WaveyDipole]

I think in his design, the receiver is supplying power to the Arduino as it would have done to the original keypad. He says he is using an ATmega88. It should be possible, in theory to draw around 100ma. In that case, the regulator is dropping the 9v or so coming from the P connector to 5V for the Arduino. According to the Lowe manual, both power and signal travel along the same conductor. I am not sure what level of signal modulation is required to drive the circuit in the radio.

Q1(c) - bottom of R1 - does indeed provide a much greater pulse amplitude.

I should also mention that I am using a Micro board which I thought was a 3.3V board and have used a 10k resistor instead of 12k for R4. As it turns out, the oscilloscope shows a 5V high signal from the pin anyway. I have tried other values but it makes little difference, if any so have just left it at 10k.

[frsimen]

The HF225 keypad uses a SL490DP remote control IC. The datasheet for that (or the SL490B) shows the waveforms and codes for the various buttons.

I made up a controller using a small PIC device and coded it from the information given in the SL490B data sheet, plus that from the Lowe manual. It works well. Your Arduino version should be just as good, so long as you set the pulse width and timings to be the same as used by Lowe.

The regulator looks to be the correct way around, as the circuit takes its power from the HF225. Possibly the Arduino will draw too much current, though.

Paula

[SiriusHardware]

Ref: The keypad, I did the same thing years ago using a PIC. The thing which held me up was the lack of a critical bit of information which was not made clear in any of the technical information: The keypad sends the data packet more than once, and the radio will not respond unless it receives several identical data packets in quick succession.

The reason is that the original / Mk1 version of the keypad was based around a dedicated remote control transmitter chip, and of course they typically keep sending while a button / key is held down.

Lowe seem to have used this as a crude form of error detection, ie, the receiver expects to receive at least 'n' identical packets in a short space of time - if all of the packets are the same, the chances are they are intact and valid.

My PIC version sends each packet (I think) three times in close succession, so each button press results in three identical packets being transmitted.

Hopefully this is the answer to your problem.

[frsimen]

The keypad sends the data packet more than once, and the radio will not respond unless it receives several identical data packets in quick succession.

I didn't need to do this with my PIC code. Perhaps there are different versions of the ROMs in the HF225, my one works with the codes sent just once.

Paula

[SiriusHardware]

Mine absolutely would not budge unless I sent the keycode more than once. (Incidentally, mine was made for an HF-150 but I have always assumed the keypad for all Lowe models was the same.)

Wavey might also be interested in this thread regarding computer control of the HF-150 , the codes sent are similar to those from the keypad but they are bracketed by more 'intro' pulses perhaps to inform the radio that the commands are coming from an IF-150 computer control interface - and in the case of these commands, each one does only need to be sent once.

https://www.vintage-radio.net/forum/showthread.php?t=193838

The advantage of emulating the IF-150 rather than the keypad is that it can also send 'fine tune' information, so tuning precision is not limited to the relatively coarse 5-digit resolution of the keypad.

[frsimen]

The HF150 and HF225 keypad circuits are identical. Unless the pulse timing is slightly off, I would expect it to work with only one set of pulses as on my HF225.

Looking at the OP's circuit clip, there should be a diode between the input to the voltage regulator and the two collector resistors. This is to isolate the voltage regulator from the switching waveform. The original had a 22uF capacitor from the regulator input to the 0V line too. It would be worth checking the 5V at the regulator output in case it is leaping around and resetting the Arduino constantly.

Paula

[SiriusHardware]

It's certainly an interesting puzzle: Obviously, my code calls the same 'send' routine three times over, so the code will be equally badly - or well - timed each time. The timing won't improve, the more packets I send.

It would be good if someone could capture the output from a real HFxxx keypad, and if it does send packet only once then I will have to work out why I need to send it more than once.

Although, to be honest, I probably won't since it works as it is.

[SiriusHardware]

I agree with Paula's observation re: The supply arrangement, mine has a forward biased diode between the modulated supply / data line and a largish reservoir capacitor which charges up through the diode when the modulator is not pulsing the supply / data line low.

When the modulator takes deep bites out of the incoming voltage, the diode prevents the capacitor from being discharged so the minimum required voltage input to the regulator is maintained during the relatively short supply / data line pulses.

[WaveyDipole]

Thank you Paula and SiriusHardware for all of the additional information. This will be extremely helpful I am sure.

Originally Posted by frsimen

The HF225 keypad uses a SL490DP remote control IC. The datasheet for that (or the SL490B) shows the wave-forms and codes for the various buttons.

Thanks for the suggestion. I should have looked at the datasheet myself. Just been looking at it now and it does have some very useful information including how the codes were derrived. Not sure how much difference between the DP and B variants? The online datasheets seem to be for the latter. Incidentally, one of these days I will get a PIC programmer and learn how to program PIC chips.... In the meantime, I am working with MCUs. Any sggestion which PIC to start with?

The datasheet shows one of the bits of information I was looking for, namely the output pulse height. Its shown as 7.0v to 10.5v. I will need to check tomorrow whether that is what I was getting.

Originally Posted by SiriusHardware

Ref: The keypad, I did the same thing years ago using a PIC. The thing which held me up was the lack of a critical bit of information which was not made clear in any of the technical information: The keypad sends the data packet more than once, and the radio will not respond unless it receives several identical data packets in quick succession.

The reason is that the original / Mk1 version of the keypad was based around a dedicated remote control transmitter chip, and of course they typically keep sending while a button / key is held down.

Lowe seem to have used this as a crude form of error detection, ie, the receiver expects to receive at least 'n' identical packets in a short space of time - if all of the packets are the same, the chances are they are intact and valid.

My PIC version sends each packet (I think) three times in close succession, so each button press results in three identical packets being transmitted.

Hopefully this is the answer to your problem.

I did read somewhere that the keypad sent the code repeatedly while the key is pressed down, although I didn't translate that quite into what you are saying here. The datasheet shows the timings including the interword timing, so I can make some adjustments to my code to replicate that behaviour.

The timings from the information provided by Jez in the linked thread as slightly different to the ones used by the author of the article I linked, but only very slightly (2100, 3150 vs 2040, 3020). The additional 3 pulses at the front also seems to mark a difference, but they are not shown on the SL490 datasheet which is curious. Nor are they shown in the trace example in the HF-150 manual. Incidentally, I searched for a keypad for the HF-150 and the results that came back seemed to show the same keypad as for the HF-150, so that is a puzzle. Makes me wonder whether those 3 extra pulses shown by Jez are spurious?

I see also, that the threead has a linked keycodes PDF which shows codes for fine tuning. Not sure whether I will be able to make use of those on the HF-225 or not, but useful to have as a reference nonetheless.

Originally Posted by SiriusHardware

It would be good if someone could capture the output from a real HFxxx keypad, and if it does send packet only once then I will have to work out why I need to send it more than once.

There is a ZIP attachment in that linked thread which shows the timings in a graph. I was initially confused by the presentation until I realised that it is showing two different packets. Unfortunately, not one of the included oscilloscope screenshots shows the full packet. But yes, it would be useful to see the complete transmission.

Originally Posted by frsimen

Possibly the Arduino will draw too much current, though.

The current draw for the SL490B is 16ma@10V. The keypad is supplied via an 82ohm 1W resistor directly fro B+. On the HF-150, its two 39ohm resistors in series rated at 3/8W. The current draw for the Micro is around 50mA@5V which is a bit more than the SL490, but might theoretically still be possible to get away with. The power level would be on the threshold of a 1/4 watt resistor, so the margin with a 3/8W is a bit tight. An ESP32-C3 reportedly draws 110ma and the power draw would be 0.55W so well over the limit for a 3/8w resistor, although the 1W in the HF-225 might e fine. The Mirco should be fine if powered and controlled over USB, which is what I am doing at present with my prototype. It looks like any WiFi device would have to be powered externally and the radio protected appropriately.

Originally Posted by frsimen

Looking at the OP's circuit clip, there should be a diode between the input to the voltage regulator and the two collector resistors. This is to isolate the voltage regulator from the switching waveform. The original had a 22uF capacitor from the regulator input to the 0V line too. It would be worth checking the 5V at the regulator output in case it is leaping around and resetting the Arduino constantly.

I see you were looking at the HF-150 circuit. The HF-225 circuit seems to omit those - I guess they deemed that the regulator and reservoir capacitor to be sufficient - but the additional diode and capacitor do make sense.

I am also a little puzzled by the diagrams of the pulses in both the Lowe manuals (HF150 manual p 13) and the SL490 datasheet, as they show a nominally low level and positive going pulses, but if the output from the chip (or Arduno) is nominally low, then (following the Lowe circuit) Q3 is turned off and Q4 therefore turned on, which would pull the voltage of the power supply down and it would rise back up on a pulse - which is what happens on my prototype. But the screenshots show inverted pulses on the output, which makes more sense.

[SiriusHardware]

From what I remember the 'normal / inactive' state of the supply / data line from the radio should be 'high' with no pulldown exerted on it, and the keypad interface pulls it 'low' for short periods of time.

[WaveyDipole]

Yes, that's my understanding of how it should work.

I also found the ZIP file at the very end of the other thread. Its now apparent that the HF-150 keypad sends 8-bit bursts instead of 6-bit to accomodate fine tuning, so yes, the pulse 'word' for the HF-150 does seem to be different to that on the HF-225. I am still reading up on the detail. I guess the HF-225 doesn't have the fine tuning capability although I see from the manual that fine tuning on the HF-225 is possible using the rotary control.

I am still trying to figure out how to select the various functions on the front panel buttons as the manual does not appear to explain this fully but I will get there.

[WaveyDipole]

BTW, the notes in that ZIP file refer to an 'integer' 6-burst sequences and fractional 8-bit sequences being sent, so perhaps the 'integer 6-burst' sequences are compatible between both radios, but the HF-150 additionally understands the 8-bit sequences?

(Getting rather frustrated with this editing time limit. No other forum seems to have this? Sorry for the additional post. Would have otherwise just updated the previous one.).

[SiriusHardware]

I should stress that the device under discussion throughout that thread was the IF-150 which was Lowe's computer control interface for the HF-150 and possibly other radios.

To the best of my knowledge the original keypad does not send the final two 'fine tune' characters, which consist of two bursts, a 5-bit 'Fine tune information follows' command (11111) followed by an 8-bit value. My homebrew one certainly does not, but it still works.

You queried whether the three 'leader' pulses shown in scope captures in that thread were some kind of artefact or error, no they are not, they are consistent but they are specific to packets sent by the IF-150 computer control interface, and are not needed / not present in packets sent by the keypad.

There is of course no reason why your keypad should not generate packets which conform to those which were output by the IF-150 rather than the shorter 5-character messages sent by the keypads if you want to be able to manually enter frequencies with higher than 5-digit resolution.

[SiriusHardware]

Regarding additional functions such as selection of mode (AM, USB, LSB, etc) from the keypad I think from the user point of view it probably goes something like this:

-Hold down a non-numeric key (possibly '*')
-Momentarily press one of the other keys to select the mode
-Release the '*' key.

I didn't actually implement this feature on mine, all I can do with mine presently is enter 5 frequency digits.

Another thing I'm dimly remembering - I think the radio doesn't update its display / frequency until all 5 digits have been received from the keypad, so if you are only sending single digits during this testing phase that may be another reason why you aren't seeing any response.

[WaveyDipole]

Originally Posted by SiriusHardware

I should stress that the device under discussion throughout that thread was the IF-150 which was Lowe's computer control interface for the HF-150 and possibly other radios.

Yes, I gathered that, eventually.

Originally Posted by SiriusHardware

To the best of my knowledge the original keypad does not send the final two 'fine tune' characters, which consist of two bursts, a 5-bit 'Fine tune information follows' command (11111) followed by an 8-bit value. My homebrew one certainly does not, but it still works.

You queried whether the three 'leader' pulses shown in scope captures in that thread were some kind of artefact or error, no they are not, they are consistent but they are specific to packets sent by the IF-150 computer control interface, and are not needed / not present in packets sent by the keypad.

Ah, that would explin the same keypad for both models. I had some notion that the keypad on the HF-150 could control fine tuning. I think I realised this morning that the 3 bits are not an artefact, but didn;'t realise they were not sent by the keypad. Of course, whether that works on the HF-225 would depend on what the firmware is programmed to do.

Originally Posted by SiriusHardware

Regarding additional functions such as selection of mode (AM, USB, LSB, etc) from the keypad I think from the user point of view it probably goes something like this:

-Hold down a non-numeric key (possibly '*')
-Momentarily press one of the other keys to select the mode
-Release the '*' key.

I didn't actually implement this feature on mine, all I can do with mine presently is enter 5 frequency digits.

Does that mean that alternative function selection requires the keypad?

Originally Posted by SiriusHardware

Another thing I'm dimly remembering - I think the radio doesn't update its display / frequency until all 5 digits have been received from the keypad, so if you are only sending single digits during this testing phase that may be another reason why you aren't seeing any response.

I did read a bit about that. It seems to depend on the frewquency. Anything above 3000 does not require and enter, anything below does. The manual does appear to suggest that digits appear as they are typed, but I have also tried entering a full frequency and enter. I also tried to send the clear command, which is supposed to clear the display? Perhaps only once typing digits has begun? I didn't avctually get anything at all come up. Haven't tried multiple bursts yet.

I wonder if someone can help me understand what this means from the datasheet please. I am interested in the two delta lines. The 2/3 are the pins on the IC, but as I understand it a delta is a difference so is it generating a differential signal of between 7 and 10.5V on the two pins? None is designated as ground and 3 iis connected to the transistor base. I am trying to understand the output graph in the context of the table data. The graph shows 0 to whatever the height of the pulse is.

The test circuit in the datasheet is interesting because it has capacitors on the output and pull-up resistors on both outputs, although with differing values so I would like to understand what would be seen on the scope? It can't possibly match the graph? In the IR version of the circuit, pin 2 is used (pjn 3 is n/c) which would have to be sending positive pulses to flash the IR LEDs. In the case of the keypad pin 3 is used, so wondering whether this would produce an inverse signal?

[SiriusHardware]

Does that mean that alternative function selection requires the keypad?

If you mean changing modes, (AM, USB, LSB etc) then no, that can be done from the front panel buttons although my knowledge is specific to the HF-150, the only Lowe model I have. I would imagine the HF-225 user manual must be available online somewhere.

If you are entering less than five digits you can terminate the 'entry phase' early by pressing 'Enter' which on the keypad is either '#' or '*', I can't remember, but if you enter five digits in succession (and I'm talking about actually pressing keys on the keypad here) then the 'enter' key press is not needed, the display updates upon entry of the fifth digit.

You've got me doubting myself now, so maybe I'll dust mine off tonight to either confirm or contradict what I have just said.

[SiriusHardware]

Regarding the outputs I think you are probably correct that pin 3 sends out a waveform which is the inverse of the waveform sent out on pin 2 - I suppose possibly so that the +/- swing on those outputs (relative to each other) can be used to provide a greater drive strength to whatever output transducer will be driven, also possibly to provide a symmetrical +/- signal for the modulation of an RF transmitter, etc.

[WaveyDipole]

Originally Posted by SiriusHardware

If you mean changing modes, (AM, USB, LSB etc) then no, that can be done from the front panel buttons although my knowledge is specific to the HF-150, the only Lowe model I have. I would imagine the HF-225 user manual must be available online somewhere.

No, I am aware that the receiving mode can be selected using the rotary control. I was referring to the buttons which appear to be marked with several functions each: some above the button in black, some in red, and finally some below the buttons. I have figured out the ones in black along the top. Some work by direct press, others as a toggle. I think the bottom ones relate to memory but need to read up some more on that, but I have no idea about those marked in red.

My radio just goes dead when I select FM. Not really investigated that yet.