DT203 - LED's and Switches on a SimmStickTM Bus.
This is the first Input/Output board that everyone wants and needs. Something to flash a LED to, and read a switch from. This board can monitor 24 SimmStickTM bus signals and output the results via the LED driver chips to the 24 individual LED's if required.
4 Momentary and/or 8 LINKED switch positions can be easily connected to any bus signal.
The signals monitored by the 8 LED's with E1 ULN2803 chip are:
NOTE *** If your DT203 is only ever going to be used with an 18 pin PIC chip, then the components associated with signals D8 to D15 don't need to be installed. This is E3, the 8 Resistors next to it, and the 8 LED's next to them.
1 by DT203 PCB
Switch signal connections can be done with permanent jumper wires, or two strips of single row male header pins and female jumper leads or clips. This is done with a strip of 24 pins and a strip of 8 pins.
If you use the header pin jumper principle, it means that wiring alterations can be
done very easily.
All hand assembly should be done by installing the shortest height components first.
I would suggest:
Then insert your 3 chips. You are finished.
NOTE **** A small artwork error has been found on this board. (My fault!, but keep it quiet.) The linked Switch positions SW5 to SW8 don't have the 10K pull-ups connected to the links. This amounts to 4 small .1 Inch long tracks missing. Small jumpers can be added to the solder side of the board if these last 4 switches are to be used with the links.
Date: Fri, 30 Jan 1998 19:21:04 +1100 From: Don McKenzie firstname.lastname@example.org To: Jim Moulton email@example.com Jim Moulton wrote: > > Dear Don, Bits from you arrived today, thanks. > > I'v just had a very frustrating couple of days with problems with RA4 > using your dt001, dt101 and dt 203 and have at last found the problem > The pull_up resistor on RA4 on dt101 is too big. > > To read in a logic 1 on RA4 the voltage must be atleast 0.85 Vdd (ie > 4.25V) > The input current drawn by an input pin of ULN2803 on dt 203 is 1.35ma > max > Thus the pull up resistor needs to be (5-4.25)/1.35 k (ie 560 ohms > not the 10k provided on dt101) > I have added 560 ohm to the dt203 as this is the board with the > problem load (ie the ULN2803) > what do you think ? > Plenty of code will work; > the problem is for reading the RA4 pin not > writing to it. > eg bsf PORTA,4 pin goes high > (as it can with the r pull-up and ULN load) > other code > bsf PORTA,6 RA 6 goes high and RA 4 pin goes low !!! > this is because bsf etc is read/modify/write and when it reads > it sees a '0' on RA4 and this second instruction actually > affects RA4 I'v deleted my test code but it is simple to > demonstrate the affect. > The figures I quoted are from the data books. > Jim Moulton > R.M.B 2128 > Colcott St. > TIMBOON, 3268 > PH: 03 55983544 I can show you a set of standard boards ticking away on a walking LED program here on an 84 without problems on RA4, but I have to believe you of course Jim. I feel to install it on the board that displays the load problems is the correct solution. So that your frustrating couple of days is put to good use, I'll add this message to the hardware html file of the DT203 so that others will benefit. Cheers Don... BTW. I have found when using FED Basic that if you load SCL and SDA with a DT203 LED's and Switches board, it may not run. Remove the first ULN2803 chip for initial tests. Don...
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