Any diagram for expansion port EAR input?

[Lynxman]

Hi. I've refurbished an old grey +2 and am enjoying it, but would like to load games from my phone. Is it possible to create an EAR input via the expansion port? I'm gonna build a Kempston adapter for the expansion port soon so would love to add an ear to the card as well. I know the 1bis has ear input but not sure if it's possible without programming.

I have tried replicating the 128k ear input and wired it to pin 34 of the ULA, but there was no response when I tried to load. I also tried this mod but the signal was audibly distorted and would not load: https://spectrumforeveryone.com/2017/04 ... rt-grey-2/

Tape loading is flawless.

[1024MAK]

I have tried replicating the 128k ear input and wired it to pin 34 of the ULA, but there was no response when I tried to load. I also tried this mod but the signal was audibly distorted and would not load: https://spectrumforeveryone.com/2017/04 ... rt-grey-2/

Adding an Ear input to a device connected to the edge-connector of a +2 (grey) may be possible. BUT you will need suitable logic gates to carry out I/O port control and address decoding and signal to data bus interfacing, and suitable audio circuitry components plus the socket. Second, the cassette pin on the Spectrum ULA (pin 34) will still read the level when the Z80 CPU tries to read the input from the new Ear input. The result the Z80 gets will be a logical combination of the two inputs, so it may not work as expected. For example if the ULA Ear is logic zero, the external Ear circuit will not be able to send a logic one to the CPU as the ULA may override it...

Is your tape deck the same type as in the article on the Spectrum for Everyone web page or is it the other design?

I suspect you are overlooking something, as there are others who have got external audio sources working with their +2 machines.

Tell me more details about how you tried a 128k Ear circuit.

Mark

[Lynxman]

My tape PCB looks the same as that one. It has the same factory mods on it too. My phone would not recognize anything on the jack with that mod so I tried an app to force output on the jack and also tried an MP3 player. I might try adding a 1k resistor over the jack to trigger the phone. The sound from the TV during loading sounded brighter than it should, and the colored frame didn't change like it should.

Here's my test circuit. Please excuse the janky setup, I had no proto pcbs, but it should work. The ground was connected to the ground pin on the tape connector on the motherboard.


I did not add the short between pin 34 and 35 as in the schematic below.

128k:


+2:

[Ast A. Moore]

Here’s a simple way of adding an audio input to a +2 for the purpose of loading software with an external audio source:

https://youtu.be/qUIv-A_DOc0?t=735

[Lynxman]

I've seen that video, but it seemed a bit complicated compared to the 128k input. I don't have an oscilloscopt so I didn't feel like changing the circuit. I will get a scope sono though.

Here's a shot my my unit right now:
https://imgur.com/527xiK6

I'll try the simple wired mod again.

[Ast A. Moore]

I'll try the simple wired mod again.

The important bit is the clamping diode on the ULA’s EAR input used in all previous and subsequent Spectrum models. The ULA doesn’t like the input signal to go negative. It’s up to you, but you risk damaging it.

[Lynxman]

There's a diode on the tape deck board though isn't there? I'm doing the spectrumforeveryone mod again.

Still doesn't work with the wires soldered to pin 5 of the tape dck chip and ground. Too low volume and distorted compared to what I expect. An old school tape deck might be loud enough to work. A 3,3k resistor across the inpupt did get it to trigger my phone though.

[Ast A. Moore]

There's a diode on the tape deck board though isn't there?

No, not as such. The amplification circuit is designed in such a way that the signal only swings to positive values.

Still doesn't work with the wires soldered to pin 5 of the tape dck chip and ground. Too low volume and distorted compared to what I expect.

The reason for this are outlined in the video I linked above—mismatched impedances.

[Lynxman]

I'll have another go at it when I get a scope and can see what comes out the other end.

[1024MAK]

My tape PCB looks the same as that one. It has the same factory mods on it too. My phone would not recognize anything on the jack with that mod so I tried an app to force output on the jack and also tried an MP3 player. I might try adding a 1k resistor over the jack to trigger the phone. The sound from the TV during loading sounded brighter than it should, and the colored frame didn't change like it should.

Here's my test circuit. Please excuse the janky setup, I had no proto pcbs, but it should work. The ground was connected to the ground pin on the tape connector on the motherboard.


I did not add the short between pin 34 and 35 as in the schematic below.

You don’t need the 10nF (0.01uF) capacitor (there is already one on the +2 board) and you don’t need to connect a short between the ULA pins.

I suspect the problem is that your phone can’t output a loud enough signal due to manufacturers limiting the level to prevent daft people from damaging their hearing.

One other thing that can trip people up, 3.5mm mono plugs are not completely compatible with stereo 3.5mm sockets AND 3.5mm stereo plugs are not completely compatible with mono 3.5mm sockets. Only use a mono plug in a mono socket and only use a stereo plug in a stereo socket.

Mark

[Lynxman]

Yeah I'm using a stereo cable with a stereo socket, with the signal pins connected on the socket. A mono jack in the phone will short one of the channels to ground.

[1024MAK]

Question, do you still wish to retain use of the built in cassette desk?

Does your multimeter handle audio AC frequency signals?

Mark

[Joefish]

Am I right in thinking that if you disconnect and do away with the internal tape player, you can just jack an external cassette player into the EAR pin (pin 4) of the internal cassette player connector?
(Although MP3 players tend not to have enough volume, a regular cassette player does).

[Ast A. Moore]

Am I right in thinking that if you disconnect and do away with the internal tape player, you can just jack an external cassette player into the EAR pin (pin 4) of the internal cassette player connector?

On a +2 or +2A? On a +2, I don’t recommend it. Better go with the mod in the video I linked above. A +2A requires a much simpler mechanical mod (cutting a trace and adding a single jumper wire); then you can simply use the existing 3.5mm jack (with a stereo lead). The mod effectively turns it into a +3.

[Lynxman]

If the Ear mod on Spectrumfor everybody isn't safe for the ULA then maybe someone should inform them. Probably a good thing the phone level is so low. I can take the chance one more time and look at pin 34 with the scope with low level from the phone connected as per the guide and see if the signal is just positive.

I have to order components to build that circuit but I might just order the stuff I need. I have a bluetooth cassette adapter on the way which I will try as well.

[Ast A. Moore]

I have a bluetooth cassette adapter on the way which I will try as well.

That might be the safest and easiest option. In fact, by way of experiment when I was testing my turbo loader, I cobbled together this thing and it worked like a charm (on a +2A):



Thought fiddly to find the correct position of the head and hold it in one place, it cost me absolutely nothing.

[1024MAK]

Years ago I got a “proper” cassette adapter, from of all places, B&Q, it was in their bargain bin for I think £2.

Nearly all audio signals are AC and switch between positive and negative. A DC offset is avoided on all external input or output connections, as it can mess up other devices that may be connected to it.

For production, a 1N4148 signal diode needs connecting in parallel with resistor R102. Anode to 0V and cathode to ULA pin 34. Then you can feed an external audio signal into pin 4 on PL12, the tape deck connector.

If your external audio source cannot produce enough volume (voltage) and you don’t want or need the original cassette deck to work, remove resistor R102 (but make sure the diode is still connected). This may still not be sufficient for an weak external audio source. In which case, you need to use an amplifier.

Mark

[Lynxman]

Is there any reason why I can't connect the phone to the pin on the head in the tape drive directly?

[Lynxman]

Here's what it looks like after the 128k input circuit I cobbled together earlier with the phone volume at maximum, loading Knight Lore. The clamping diode is just one I salvaged off something so it might have too high of a forward voltage (0,56 V)for this as there's about 200 mV of negative voltage getting through.

[Lynxman]

I made the circuit from JoulesperCoulomb's video and it works fine. I removed the 5V input reverse polarity protection diode after the photos were taken. I actually struggled first because one of the 0,02uf caps on the inputs were bead and evenually failed completely but once I found that and replaced it it worked well.

I made it small and the pcb fits ncely on top of the tape deck PCB, hiding it from view when the Spectrum is opened. The tab over the power port was broken off on my Spectrum so I hot glued a jack there for input, which also makes all wires short since it' right next to the PCB over the tape deck PCB.




I checked the output with my scope and it's about 2,5 V square wave and all positive, like in his video.

[Ast A. Moore]

I checked the output with my scope and it's about 2,5 V square wave and all positive, like in his video.

That should be plenty. Congratulations.

[Lynxman]

I received my cheapo Bluetooth cassette adapter too now and have tried it. It's not as reliable as the EAR input circuit. I had to modify it to get it to work well. The little rubber drive wheel would jam and lock up the tape drive, and the head was crooked and not centered. I also lubricated the gears slightly. Not sure if the gears and the drive mechanism is even needed but it's smooth and doesn't jam now. It came with a mic which also serves as the on switch. I soldered on a little switch instead so that I don't have a microphone sticking out. It's convenient to not have to use a cable to load games though.

[Ast A. Moore]

Not sure about the +2, but on the +2A you don’t even need to press PLAY on the Datacorder to load games. The circuitry is active all the time.

[Joefish]

Thread from the Dead Question -

...

128k:


+2:

If I completely rip out the cassette player board from a grey +2, swap that 390 grounding resistor for a 1K with a diode back up over it, haven't I then got the same cassette input circuit as a 48K Speccy? (From pin 4 on the now unused cassette connector, I mean).
Or maybe parallel piggy-back a 470 on the 680 to bring the 680:390 resistor pair down to the same ratio?

Ah, wait, no, there's then no capacitor actually in-line in the circuit. But can that then just go in anywhere? e.g. between a hypothetical cassette input jack socket and that there pin 4?

(No, I'm not going to build a whole new amplifier - it's got to be simpler than that!)

[Ast A. Moore]

If I completely rip out the cassette player board from a grey +2, swap that 390 grounding resistor for a 1K with a diode back up over it, haven't I then got the same cassette input circuit as a 48K Speccy? (From pin 4 on the now unused cassette connector, I mean).

Well, yes, aside from the capacitor, which is there just to remove any DC offset. If fact, looking at the values of the components, they are identical between a 48K Speccy and a Toastrack.

Ah, wait, no, there's then no capacitor actually in-line in the circuit. But can that then just go in anywhere? e.g. between a hypothetical cassette input jack socket and that there pin 4?

Technically, yes, although it might created some unwanted filtering via an RC circuit.

But why not replicate the circuitry exactly? It’s just a few of components anyway, and half of them are already on the board.

P.S. On my +2B, when I modded the 3.5 mm plug to accept an external audio input, I had to bypass C200 altogether. Otherwise, nothing would load with the weak audio signal produced by my phone or computer. (C200 is still in-circuit when loading from the built-in Datacorder, though.)