VINTAGE BEEB HARDWARE PROJECTS... DISCUSSED...

Been reading up on this, the Beeb can accept voltages of 0v - 1.8v on the analogue port so there needs to be a way of dropping the voltage of the sensor down from 5v
More thought required.

 

There's no 5V line on the beeb?

 

Hi Paul , Richie

Thought Added
There is 5V, however if you look at the circuit diagram of the analog port it shows three diodes, from ground via a 2.7K Ohm resistor to 5V, with a 1uF cap across its afairly cheap method of getting 1.8V, due to the voltage drop across the three diodes, and it is this thats used as a referance for the ADC chip on pin 8. hence max reading at 1.8V..
so a reading of 1.8V would give a value of 255 as data on the ADC. Therefore each value from 0-255 equals 0.00703125V so for a reading of say 100 the voltage equals 0.00703125 x100 = 0.703125V for 120 0.00703125 x120 = 0.84375V
all thats needed is a divider network to reduce the maximum 1.8V input, and that from the Methane sensor of 5V at its maximum ( I presume not checked sensor info.)
See below


Above we see Vin in our case from the Sensor to Vout the input to the Beeb ..


The relationship stays the same i.e. 1.8V is 0.36 of 5V our resistor network must match this so should we plug into the formula 0.36 = R2 divided by the Sum of R1 + R2 so 564 / 1000+564 = 0.3606 so close enough.

1000 Ohm and 564 Ohm; realistically we don't want to 'load' the sensor output with a low resistive value, and would want standard value resistors ...
Trying to find values that would work that are standard resistor values try R1 as 4700ohm or 4K7 / 4.7K and R2 as 2700
or 2K7 / 2.7K for 5v input this give 1.82 V output so very close relationship 0.3648
But we can get closer by adding a third resistor
For something exact add a 100 Ohm resistor in series with R1 so 4700+100(R3) = 4800 and R2 at 2700 this give exactly 1.80V for 5V input relationship 0.36 exact ..
I await Richie's results ..

 

I was right with you Graham up to about word 10 and then it all looked like gibberish

 

O.k but I was trying to explain ... maybe not very well !!!! just use three resistors wire to analog port and enjoy ...

 

Oh the explanation was good, I'm just too thick to understand most of it

 

Yes indeed, consider yourself a teacher as it were, I mean I jest re the understanding, I understand little bits but I don't profess to be an electronics guru so there's stuff I have no clue about, you put a circuit in from of me with chips etc in the I'll look at you with that dumb look. I'm no nand gates person, hell I never used that sort of coding when I did code, it was all very basic assembler ie LDA #05 STA $D019, I was stumbling with setting bits but I could do some stuff.

I think my time may have passed to go back and try to improve my understanding, pain and stress are less than wonderful for memory and like others on here I'm in pain 24/7, I do what you guys do, smile and bite my lip.

What can you do..Get meds to put you in zombie mode, NO THANKS, I'm still moving and talking..That will do..

So Graham, you carry on quoting the details, they are dead useful for others and hey, maybe one day my one brain cell will look at stuff and get a better understanding...

Caveman Paul out...

 

I guess we all have our own problems as we aren’t getting any younger, I'm thankfully not in constant pain, but I have some idea of what living on pain killers is like. I had a succession of three back operations about 11 years ago, and thankfully; there are no nerve endings in titanium.
However the preceding 3 to 4 years weren’t great, especially as my family were younger and all lived at home, I was holding down a decent job, etc Again I was lucky as I ended up practically free of pain, I was paid in full during the 6 months I needed to recuperate off work, and supported when returning, I guess they just wanted me back where I could be of use. Certainly I headed a number of successful projects when back, and apparently saved millions so I guess it must have been worth paying for my time off. Funny how it felt more like a family rather than what became a huge company, I guess about 300-350 people swelling to more like 16,000 employee’s during the time I was there.
Currently having good and bad days, sometime lucid and have good understanding and get up and go, the next day nothing I seem to do, read or watch makes sence. so more frustration than pain as I'm aware of it.

 

Paul well setting bits ...
just AND with the value you already have
LDA #5 ;(b00000101)
AND b11000000 ; Setting bits 7 & 6 'A' should now read b11000101 you didnt say what bits..
STA $D019 ;

Paul we only learn from our mistakes, as long as we don't repeat those same mistakes of course, and nobody is to old to learn new stuff, sometime we just have to chuck out what we don't need; to replace it with something new ..

 

Sorry to hear Graham, days like that are hard to go through..

As soon as stress hits me then I get very like that, my poor old head with it's depression starts telling me bad things to do to me but I'm aware enough to not really listen. It's not voices, just my depression takes over to a degree. The last thing I need is to hear other voices in my head, its busy enough as it is

Glad you are pain free, backs are troublesome items and rarely let you off the hook when they have issues so it's nice to hear that you did get better.

Right, off to work out why Numen demo won't work off the AVG (for me) yet runs fine from SD-Max..Can't be the U1MB as it works off the SD-Max, everything else seems to work yet others with the same firmware get it to load direct from the cart..Weird..

As for the AND scenario, I was just using random code, my maths was never good, need to read up on how AND OR and the others work. I guess its the whole notion of why you have to set bits that sort of puzzles, I'm just used to slapping numbers in addresses. I sort of see why but then I start to get confused....Put it down to maths IQ -200

 

Sounds like a conflict some place, but you are likely to know more than me on that one.. I just get too technical are boring unfortunately Oh and haven’t learnt from that ...

 

Graham, you be as tech as you like me old mate, just because a dozy sod like me can't understand some of what you mention only reflects on me, your tech is greatly appreciated and clearly by the people you work(ed) for. Solved the Numen demo issue, crap free micro SD that came with a C64 SD adaptor for free. Made in taiwan unbadged rubbish, went to get some data of it in the PC and it has weird files with pathing errors galore...

My nice genuine Sans Disk SD works perfectly.

All I need is a cure for my neighbours...Bazooka anyone?

Just came back in from dropping my daughter to the station (Dad's a Cab) and I could hear the moron woman talking to a friend saying "Oh, the reason I live here is" as if the place is a much wanted area full of wealth and niceness. She came here because Southall was way too annoying for her (which it is, too busy, too loud) and now she's on an estate infested with gangs and drug dealers, a convicted rapist mere metre's from where I sit and the haunt of many child molestors. Hell we even had the first two british convicted of preparing for for acts or terror. The white ginger headed moron and his Pakistani mate who also happened to be a drug dealer. They lived here and walked past my window daily...

Does all that not make you want to up sticks and move here.....What do you mean NO...