VOGONS


Reply 20 of 26, by dionb

User metadata
Rank l33t++
Rank
l33t++
matze79 wrote:

Right, looks like my Google-fu was sadly lacking here. Your project is both vastly more elegant and mature 😀

That said, I'll still soldier on here, half the reason for doing this is learning as I go 😉

Reply 21 of 26, by VioletGiraffe

User metadata
Rank Newbie
Rank
Newbie
dionb wrote:

That said, I'll still soldier on here, half the reason for doing this is learning as I go 😉

Took me some staring to figure out whether you said "soldier" or "solder" since both were equally fitting.

Reply 22 of 26, by VioletGiraffe

User metadata
Rank Newbie
Rank
Newbie

So according to Wiki, RS-232 serial port uses +3 to +15 volts for logical HIGH and -3 to -15 V for LOW. I wouldn't be surprised to see +/-12 being used by PCs since -12 V is the only negative voltage produced by AT/ATX PSUs. I've also read 74HC and 74LS datasheets, and the min/max input voltage is not even listed in "Absolute maximum ratings". I assume no one in their right mind thought these parts may be used outside of the intended +5 V digital environment. Finding an optocouple device that can withstand -12 V is also challenging.

Reply 23 of 26, by dionb

User metadata
Rank l33t++
Rank
l33t++
VioletGiraffe wrote:

So according to Wiki, RS-232 serial port uses +3 to +15 volts for logical HIGH and -3 to -15 V for LOW. I wouldn't be surprised to see +/-12 being used by PCs since -12 V is the only negative voltage produced by AT/ATX PSUs. I've also read 74HC and 74LS datasheets, and the min/max input voltage is not even listed in "Absolute maximum ratings". I assume no one in their right mind thought these parts may be used outside of the intended +5 V digital environment. Finding an optocouple device that can withstand -12 V is also challenging.

OK, but you're talking about input from the serial port. That's what the 7805 is for, it accepts anything up to 19V and outputs 5V (with a resistor between it and the Arduino for extra security), converting the RTS signal into something safe. The 74LS00 is on the output to the serial port, so it's not exposed to whatever voltages the other side uses to signal with. It just outputs its 5V towards the serial Rx port.

Reply 24 of 26, by VioletGiraffe

User metadata
Rank Newbie
Rank
Newbie

Oh, you're right, thanks, somehow I was thinking about it backwards. So the problem is even more complex - converting 0/5 V into +/-12 V.
I think I'll try a purpose-designed MAX232 IC for this, the circuit will be even simpler.

Reply 25 of 26, by dionb

User metadata
Rank l33t++
Rank
l33t++
VioletGiraffe wrote:

Oh, you're right, thanks, somehow I was thinking about it backwards. So the problem is even more complex - converting 0/5 V into +/-12 V.
I think I'll try a purpose-designed MAX232 IC for this, the circuit will be even simpler.

Don't think that's necessary - you just quoted RS232 spec as accepting anything from 3V up, so the 5V from the 74LS00 (or other source) should be fine.

Reply 26 of 26, by Eimer

User metadata
Rank Newbie
Rank
Newbie
Caluser2000 wrote on 2019-10-07, 21:50:
VioletGiraffe wrote:
Caluser2000 wrote:

Seems overly complicated. I use one of these20191008_101546[1].jpg

A passive adapter? It would only work with a dual-interface mouse (COM + PS/2), I don't have nor ever seen one. I'll much rather use a good modern optical/laser mouse.

Works just fine with my opticle ps/2 mice and usb mice with ps/2 mice adapters. Obviously you haven't been around computers that long.

I have several of these, but they don't work with mice that only support PS/2 as they don't have the logic to switch between serial and PS/2 mode.
unfortunately none of my mice support this.