In my ongoing battle with LEDs versus the sunshine, I have finally made a latched 16 character 5 x 7 text display.
With the LEDs on 100% of the time ( as opposed to multiplexing ) I now have a sign that is clear from 100m away with the sun shining straight on it.
I am using the oldish MM5451 chip with 35 outputs ( 2 LEDs in series on each output ) running at 25mA per pin .
I can get away with 25mA because the bitpattern I have written for the characters only has a max of 20 outputs on at any time ( for upper case B ) and also with 2 red LEDs in series, the chip only has to drop 1 volt.
The problem arose because unlike the TPIC6B595 shift registers, ( which I use for the 7 seg numerical displays ) , there is no data out or latch on the MM5451s so you cant just daisychain them.
So after 3 years of being converted to Arduino, I pulled out my shoe box of hundreds of CMOS chips, ( which had been my mainstay for 30 years ) and dug out some CD4013 flip flops.
It gets worse I am afraid, not only am I using CMOS logic to step through the display chips, but I am also using MickeyMouse logic ( resistor/diode AND gate ) to inhibit the data to the unselected chips.
I am using a schottky diode so only lose 200mV, but it saves another chip on each display pcb.
I somehow feel I am being unfaithful to my new micro knowledge, but its working very well. And of course the 328 chip tells it what to display !
The chip cost about US$ 4 each, but they use constant current to save resistors, and I am pwm the current set pin for dimming.
"Just kiddin', whatever works works eh? But please tell me you aren't using the DIP package"
I was thinking of a 12AX7 (ECC83) to start with ..... 8)
I am using the 5451 because I need all 35 outputs for the 5x7 display.
I just have a seperate clock and data from the 328 which goes to the first display boards flip flop, which allows data to that boards chip for 36 bits, then I send a zero and clock it, so that the ONE goes through to the next boards flip flop.
I didnt bother with a reset for this as I just send through 16 zeros to make sure its clear before I start commutation .
Don't forget to backup your schematic in PCX format to a 5 1/4 inch floppy disk along with a WordStar file that describes it's function. This way it will be available for generations to come.
Then draw it all out for a phenolic PCB, etched in ferric chloride, leaving enough clearance around the PCB mount 9pin valve sockets for ventilation.
Oh and don't forget to leave enough length in the lead to reach the valve top cap.
This has made me realise how my electronics has changed since getting into Arduino, I still have drawers with all the various values of resistors and caps, but only use a couple of values now, and I must have 500 or more CMOS and analog chips, hardle ever used.
I used to have a shelf full of databooks, but I dumped them on the last house move, its quicker to find a datasheet on the net.
Boffin1:
This has made me realise how my electronics has changed since getting into Arduino, I still have drawers with all the various values of resistors and caps,
Yes data books are pretty much a thing of the past, I used to have 100s.
BTW, the forum is not longer notifying of new posts, I just re-found this thread by accident, so I'm guessing there won't be as many responses to all threads from now on unless that gets fixed.
Hi, I don't know if any of you guys had this problem during the game last night but my Nipkow disk kept getting out of sync.
I think we have someone in the neighbourhood who has a spark transmitter, i though I heard it arching away last night.
Going to ring the Baird TV techs in the morning, just got to remember to shake the phone hand piece first to loosen the carbon in the microphone.
Isn't the modern world great.
What!!!!!!!!!!!!!!!!!!!!!!!!!!!!!s with the format code???????????????
Tom......
PS Just got the gas bill, got to get the kids to turn the lights off when they leave the room.
