The Sinclair QL Forum

Here is my hacked hall effect switch keyboard with shaved prototype PBC plugs for the membrane to main QL board connectors on the left. I used old telephone cable for keyboard to QL connections and have to pick up 5V from the QL board to supply the hall effect switches. I don't have a specification for the switches so does anybody know if the QL 10 K pull down resistors need to be 1K like on the original donor keyboard circuit for the hall effect switches to work?
Now I have to figure out the best way to test it so it doesn't blow up my QL.

I wanted more information about the hall effect switches and found these two resources that I couldn't find last time I looked.https://deskthority.net/wiki/Micro_Switch_SD_Series
https://telcontar.net/KBK/Micro_Switch/SD#output
It looks like a hall effect switch is not necessarily a switch although the three terminal one does seem like a momentary type. Mine is R4A3E with 40 and 4R on the left & right of sensor with the R in grey but there are '?' all over the sites on the bits I want to know. My impression is the switches are quite high current and originally they were driven by a 74154 with 1K resistor pull downs in series so don't look directly compatible with the QL 3K & 10K set up.
I checked the QL output signals that are all the same but the first line is different looking like it doesn't pull down low enough. When I tested the fixed QL with a wire short in place of the membrane I had the impression it wasn't very consistent but put it down to my wire poking because all the lines did give characters. So the first line needs investigating but the others would show if my keyboard works or not.
Confident the keyboard wouldn't damage the QL I plugged it in and it doesn't work. Checking the drive signals with it unplugged they are the same so no damage caused.
Things don't look promising because the switches originally worked with 5mA and the 8049 is limited to <2mA so needs buffering.
Any suggestions? Time for a cup of tea.

Ruptor wrote:Any suggestions? Time for a cup of tea.

Obviously not but the tea seems to have worked. The problem is I need buffers so if I have a PIC transfer the output lines it can read them in and pass them out at up to 25 mA on any one pin then I can put 1K pull down resistors keeping all the stuff at the hall effect keyboard end and problem solved. It also allows me to change the on time of the drive signals, have any key matrix like press two for one and give a serial output I want for another 68010 board if I get around to building one. I am now a man with a plan.

Back again with stupid questions. I assume the standard QL uses just the keys listed on the matrix but do QL programs use control and alt keys to give other codes? I have a slight change of plan as it seems I can use any computer as a keyboard using a teletype program to send serial data via USB and use a USB to serial converter to interface my QL based PIC that receives serial and transfers it to QL parallel input. I just need to know what the table is for converting ASCII to QL key inputs if someone could enlighten me. Having a PIC on the QL key inputs also brings the possibility of a PS/2 keyboard input that would be in parallel with the serial line.
Have to get off this site it is knackering my already noisy knackered cpu fan.

You mean something like this?
viewtopic.php?t=4012

Stephan

Maskenlos wrote: ↑Sat Dec 03, 2022 3:02 pmYou mean something like this?

Sort of but not so complex. I didn't consider the length of a key press, then went in a big loop thinking about key on key off status ending up deciding it was all irrelevant. All I have to do is place what ever key is received by my PIC on one scan of the QL keys. The computer terminal in the first instance gives repeats and I can do what I want on the PIC I put in my Hall effect keyboard design.

More stupid questions that someone can probably answer off the top of their head. How long does a QL keyboard key have to be present to register and how long is a scan line on for? All this is so I can get a simple serial or SPI link from the above keyboard to QL.

Since I had no pointers to the required info I stuck a scope on the key scan signals and it looks like my QL is dying of old age. Here are pictures of pin 1,2 & 9 where 9 is the only one that looks like what I would expect. The key scanning looks duff to me any comments? Note the order of the pictures is 9,1,2. I dragged and dropped them in a different order.

Pin 1, 2, 9 of what?

Looks like you have some sort of capacitance in the matrix.

tofro wrote: ↑Mon Dec 12, 2022 12:28 pmPin 1, 2, 9 of what?

The 9 pin scan lines of the QL keyboard matrix without the membrane plugged in.