Help: PC joystick to Electron joystick adapter???

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Merlin
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Help: PC joystick to Electron joystick adapter???

Post by Merlin »

Hi,

I am looking for some help with adapting a 15-pin PC analogue joystick to an Acorn Electron 15-pin joystick port. I understand that the Acorn pinout assignments were decided before the pinouts of the PC MIDI/joystick port were agreed, so although they share the same connector, they are incompatible; all of the required signals are there, but in the wrong sequence...

Is there a BBC Guru that can help me put together an adapter that can allow me to use a PC joystick (or possibly a joypad) on the Electron? I have the pinouts for the Electron and the PC pinouts are easily found, but the Plus 1 Interface manual for the Electron doesn't describe them in the same language as the PC port.

Thanks
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AlanD
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Re: Help: PC joystick to Electron joystick adapter???

Post by AlanD »

Hi merlin

i have actually done this some time ago it was not a straight forward as you might imagine ,i will look through my everything ELK directory over the weekend and dig out the info if my memory serves me correctly it will require a translatoin lead which also needs somes resistors in one of the 15 way D connectors

will post the info as soon as i find it

AlanD
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Merlin
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Re: Help: PC joystick to Electron joystick adapter???

Post by Merlin »

Thanks, AlanD.

I know what you mean; the Plus 1 Manual wasn't exactly a bundle of help about directions of signals and I suspect that the voltages are different as well, compared to the PC standard that followed.
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Re: Help: PC joystick to Electron joystick adapter???

Post by Fraser »

I am also looking for one. Isn't the port exactly the same as the BBC one? I know there is a difference in sampling. The Electons Plus 1 does 8 bit samples and the BBC does 16 bit.
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Merlin
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Re: Help: PC joystick to Electron joystick adapter???

Post by Merlin »

I'm not sure, Fraser; Pin 9 on the BBC seems to be for a light pen, whereas on the Electron Pin 9 isn't connected, according to the Plus 1 manual.
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Re: Help: PC joystick to Electron joystick adapter???

Post by retroclinic »

The pinouts are different, as is the way the analog signal is sampled. On the PC interface, the analog signal is just an open ended pot to ground, and the resistance controls the duration of a timer which gives the position of the pot. On the Beeb, the pot is connected across a positive voltage, and the wiper voltage is sampled by an ADC to give a digital result.

Typical PC of the day crap cheapo way of doing things.

Mark.
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Merlin
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Re: Help: PC joystick to Electron joystick adapter???

Post by Merlin »

@ AlanD

Have you had any joy in finding that interface diagram?

Thanks
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Re: Help: PC joystick to Electron joystick adapter???

Post by MartinB »

Ok Merlin - the best way to get things moving on here is to post some outrageous technical statements, preferably with lots of errors, and then people will move in for the kill and a productive discussion will ensue :D

So, here's some notes I made.....
joystick info.JPG
joystick info.JPG (14.81 KiB) Viewed 3606 times
If you were to ignore all else and just use the two pinout schedules then you would make a short adaptor cable with a 15-way D-Type at each end (plug & socket) and that would be it. On the PC, +5v is the equivalent to Beeb Vref and 0v is equivalent to Beeb Analogue Ground for the purposes of the XY channels. On the PC, the Fire buttons (we would only use F1) switch to 0v as they do on the Beeb - I've missed the 0v off the Beeb end btw which are 2, 3 & 6.

Now, at the bottom I've shown the two XY channel connection protocols and they are different. The Beeb uses a potential divider arrangement accross Vref and Aground with a tap to the channel input. The PC however just uses a variable resistor from +5v to the channel input. Ideally then, one would crack open the PC joystick and connect the open end of each pot to a common ground (0v) pin and then this pin would equate to Aground on the Beeb. (Looks as if PC pots are 100k-ish whereas Beeb pots are normally lower I think - could be an issue?) However, if that's not practical, then something needs to be done in the adaptor cable which is probably what AlanD was referring to. I think we'd be looking at an additional resistor from the PC channel inputs (the tap) across to 0v (Aground) but the value would depend on the values of the PC pots and would need to be chosen so as not to restrict the range of movement.

Ok, that's my 10 minute take on this, jump in anytime people.... :D

Martin
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Re: Help: PC joystick to Electron joystick adapter???

Post by Merlin »

Hmm, OK... I must admit I had sort of come around to the conclusion after reading around that it would need some sort of inline interface box, with some A/D converters and maybe incorporating something like some 555 timers along with some trimmer resistors, in order to adjust the centre and sensitivity of the joystick.

/Merlin sits back and waits for the dissfest to begin....
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Re: Help: PC joystick to Electron joystick adapter???

Post by MartinB »

I don't think active circuitry would be necessary for a basic PC analogue joystick + fire button, just some adjustment to the potentiometer layout but let's see what others think. If I wasn't so tied up with BeebSID I'd have a play but maybe we can encourage others to tinker with this? Sounds like fun to me.... :wink:

(If you're thinking of more complex controllers like multi-function gamepads then yes, an active interface would definitely be necessary.)

Martin
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Re: Help: PC joystick to Electron joystick adapter???

Post by MartinB »

I've given this a bit more thought.... :-k

Beeb Vref defines the maximum voltage input to an ADC channel from a joystick and is approximately 1.8v, the minimum being as near as dammit 0v. Referring back to the blurry notes above and the PC pot configuration on the left, if we add a new resistor (shown in orange) as follows...
R mod.JPG
R mod.JPG (5.39 KiB) Viewed 3478 times
...and translate the appropriate connections across to the Beeb then this might do the trick. (0v should say 'Analogue Ground' and X/Y means either - i.e. do this on each channel)

At one end of the pot (or full travel of an axis) we will get the full Vref as for a normal Beeb joystick. At the other end, the new resistor will give us a voltage of approximately 0.08v which is not zero but may be small enough to convert as such give or take a fraction. The value of the resistor is a juggling act to allow the minimum possible value at 'this end' but not draw any significant current from Vref at 'the other end'. A 4k7 will draw approx. 0.4mA per channel or 0.8mA if the stick had both axes at 'this end'. I have assumed for this that the PC joystick is a nominal 100k ohm.

Could somebody cast an eye and comment on or ridicule : the theory, the current draw with the mod, the 0.08v minimum voltage and the assumed PC pot value. If it does all sound plausible then I can show the connections for the adaptor cable and Merlin can give it a whirl. (@ Merlin Do you do wiring, soldering etc. ?)

@ AlanD - was this perhaps what you did?

Martin
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Re: Help: PC joystick to Electron joystick adapter???

Post by retroclinic »

Hi Martin.

Nice idea, but the travel would be all in the first few milimeters of the stick. If you concider how far does the stick have to travel to read 4k7 on the 100k put, 5% of it's travel, but that's 50% of the Voltage at VRef. At half travel, IE centred, you will have 50k pull up to VRef, and 4k7 pull down to ground, so it will read around 10% of Vref, not the 50% needed.

The idea of wiring the other side to VRef is the best idea, but it does mean opening the JS. I think you'd need at least some sort of circuitry to translate the pot signal to the Beeb.

Mark.
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Re: Help: PC joystick to Electron joystick adapter???

Post by MartinB »

Well spotted Mark and you're right - I'd only considered each extreme and not what happened inbetween :roll:

Yes, if it was me I'd be opening the stick up as I said earlier but I was sure there was a way of doing it in-line. Perhaps not then....

Martin
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Re: Help: PC joystick to Electron joystick adapter???

Post by MartinB »

So Merlin, looks looks like an interface box with some circuitry or a simple mod to your joystick plus an adaptor cable. I'd go for the latter and would say sacrifice Fire Button 2 (not used on a Beeb or Elk) by connecting the open (unconnected) end of each pot to the FB2 button pin (actually the appropriate wire inside the joystick body) and then you could make a hard-wired adaptor cable to finish the job. Depends how adept you are but, if you still wanted to keep FB2 for when the stick was used on a PC, you could fit a switch on the stick somewhere which toggles the FB2 pin for Joystick A between button 2 for PC mode and the pot-end for BBC mode.

The adaptor cable would then actually be very easy if you used a solderless patch adaptor such as this.

Martin
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Merlin
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Re: Help: PC joystick to Electron joystick adapter???

Post by Merlin »

Don't worry, I'm fairly nifty with a soldering iron. It's just that the two interfaces were so different that I couldn't get my head around them.

If it's all the same to you, I won't be taking my Sidewinder Force Feedback pro to bits for this... :lol:

If you can help me with a design for an interface I am happy to find a cheap alternative joystick and give it a spin.

Thanks
Last edited by Merlin on Wed Oct 21, 2009 8:51 pm, edited 1 time in total.
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Re: Help: PC joystick to Electron joystick adapter???

Post by AlanD »

Hello Martin

I cant the find my one it must be buried somewhere but i think if me memory serves me which it quite often refuses to . That i added a 1K instead of your 4k7 and shunt the pot ( across vref/ x,y) with a 22K resistor this has the effect of making the pot non linear but i think the angular fit or response was quite poor

(the greater the ratio of the pot to shunt resistor the more non linear R verses pot angle becomes)

think i amy have also opened the joystick as it may have worked in reverse

AlanD
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Re: Help: PC joystick to Electron joystick adapter???

Post by MartinB »

@ Alan : Ironically, I did first play with the numbers for a shunt arrangement and decided that linearity was going to be a problem. Then I appear to have had a brain dump and tried the single series R. Because it was fine at both ends with a linear pot I just got seduced with delight into posting. Still, at least I had the good sense to seek an opinion before proceeding :roll:

@ Merlin : Did you start this ball rolling because you have a particular fondness for PC joysticks or would some breed of original Beeb analogue sticks fit the bill? If the latter, you could ask the folk on here and I might even have some that you could purchase for a ridiculous price representative of their quality and/or rarity :wink:

If you do want to persevere with the PC type then a cheap one that you would dare to crack open would be the best solution. I'm almost certain that a simple internal wire swap or two plus a passive re-patched cable (or patch adaptor as I pointed to) would be fine.

Martin
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Re: Help: PC joystick to Electron joystick adapter???

Post by Merlin »

Well, Electron joysticks seem to be like rocking horse poo on Fleabay and when they are there, they are bundled with other stuff that usually goes for a LOLPRICE, as you call it on here.... :lol: So... I had kind of resigned to adapting a PC joystick to fit as an alternative.

If anyone has any Electron joysticks on offer, please let me know. Thanks
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Re: Help: PC joystick to Electron joystick adapter???

Post by MartinB »

'Electron joysticks' is probably a bit misleading since they're all common between the Elk, the 'B' and the Master. (The 'absent-on-the-Elk' Light Pen Strobe isn't used by joysticks.)

I have two sets of the ones below and I'd let you have the spare set for a tenner plus postage at cost. I'm not actually sure what make they are but they're quite solid and pleasant enough to use. Anyway, don't rush in - they're only on offer to you - and you should perhaps post in the Wanted section too and see if you get any other offers. I do have sets of the large Acorn original ANH01 sticks but they are LOLRARE and, apart from an occasional slip through the eBay watchers net, thay can fetch a LOLPRICE :wink:
Beeb Sticks.JPG
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Re: Help: PC joystick to Electron joystick adapter???

Post by Merlin »

Thanks MartinB, you are a superstar!!

I'll take them, but I won't be in a position to pay for them until next week. if that's OK with you, please let me know how you want payment made by PM.

Thanks

Merlin
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MartinB
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Re: Help: PC joystick to Electron joystick adapter???

Post by MartinB »

Hey, no worries - you've done plenty for the retro community with Retr0bright and AmiBay so it's good to return the favour =D>

I got both sets in 'bundles' so I've no idea what I paid for them but as you say, they're not that easy to get hold of. I've fully tested the spare set on an Elk and they're good to go and both sets are in really good nick so don't worry, there's no second best :D. I quite like them because they're just no-fuss fuctional sticks and feel well made and sturdy but that said, I'm not much of a gamer and therefore can't claim to be an expert on these things!

Anyway, I'll pack them up over the weekend and hopefully post them Monday and then I'll know how much postage is - will we suffer from the strike I wonder? I'll PM you later to talk payment (whenever btw :wink: ) and get your details.

Martin
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Re: Help: PC joystick to Electron joystick adapter???

Post by PitfallJones »

I've managed to pick up some db15 to rj45 connectors so I can swap the connections around without having to solder anything:

http://www.pccables.com/01912.htm

So just to be clear I should wire it up like this:

pc1 - bbc14 (5v)
pc4 - bbc5 (0v)
pc3 - bbc15 (X)
pc6 - bbc7 (Y)
pc2 - bbc13 (F1)
pc7 - bbc10 (F2)

(no chance of short circuiting my bbc?)

And this should give me ??v-5V where ?? could be something like 3V?
Whereas normally a bbc joystick would give 0v-5V?
Then I could read a change of position on the bbc with no other modifications but the range of values would be reduced?

Then I could open up my joystick and connect the 3rd unconnected resistor terminal (for x and y) to a ground wire somewhere internally?
Would the joystick still work on the pc?
It sounds like this change would just change the range of the output voltages on the pc thus be ok? (as the pc requires joystick calibration anyhow).

Otherwise I could try adding some resistors as mentioned before.
Could I have a diagram of the 'shunt' idea?

As you are trying to change the range ?v-5v into the range 0v-5v could you do that with a some setup of a potentiometer and a transistor? - it sort of sounds like some sort standard electronics problem...

How do you calculate the voltage on the floating end? - it seems really strange to me the pc designers would leave it unconnected - like an unfinished circuit almost.

Thanks for any help.

- PJ
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Re: Help: PC joystick to Electron joystick adapter???

Post by riscman »

Very old post, I know. But did you ever get this to work? If so how??
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