Any of you electronic wiz's know if there's a six channel or 8 channel 1-2 multiplexer out there? I found a number of four channel chips.. such as the 74LS157 - but I need six channels. What I want to replace with a single chip is this arrangement of transistors...http://members.aol.com/rick7card/flipflop.jpgThanks for any help.Richard

Richard,Your drawing looks like INP-7 is intended to direct the all the inputs either to the A outputs or the B outputs. If so, a mux isn't what you want.What is the circuit supposed to do? Mikewww.mikesflightdeck.com

I am making a radio stack with 7-segment LED displays. I have figured that I need 12 seperate banks of displays. I am driving the LEDs with M5451 latching drivers. I therefore need to send a signal only to the bank that is to be changed.The chip I am using to interface between the PC and the M5451's (A Picaxe 18x) has eight available output pins. My intention is to have output 1 send the data signal, and make that common to all the driver chips. Pins 2 through 7 will send a clock signal depending on which set of digits is to be updated, and Pin 8 will select between the A or B outputs...In other words, say I need to update the display on Bank 5. The clock pin on the driver chip for bank 5 is connected to the 3a output from my schematic above. I send from the PC a signal that bank five is to be updated, and the new value. The Picaxe's pin 8 is set low, activating the output pins to the 'A' outputs, and the clock signal is sent out on Pin 4 - which thus goes only to the clock pin on bank 5 - and the data signal is sent out to all the banks, all of which except bank 5 ignore it because they're not getting a clock signal.Richard

Now, I know a jack about electronics at this level, but have you checked www.intersil.com and their "display driver" section? They seem to have chips designed to do BCD -> 7-segment display that basically does all the work for you. I am not sure if this is exactly what you need, but it popped to my mind, so what the heck :)It's in main page -> digital -> display drivers.Also use the search to look for "7-segment" on the site and there seem to be some more stuff.//Tuomas

HmmmmmmmmmmFirst of all, it's considered bad practice to not have base resistors on the transistors. Particularly the PNP's because I don't think this scheme will work without them. If you want to "activate" the PNP's you need to have the base a diode drop below the emitter. If you pull the base to ground, then your basically shorting the INP- signal to ground through a diode and the collector voltage will only be ~.65V. BTW- Q5 & Q6 are not wired the same as the others in your schematic. The NPN's wouldn't be a problem as they are probably driving an input to a device which should be high impedance. Also, I'm assuming that the 12 pin device at the top is a connector that goes to your drivers. If that's the case, you also want pull-down resistors on those lines so you don't leave any of them floating as you select between "A & B".If I understand what your trying to do, you only need to decode which display bank you want to update with data. For something like that you could use something like a 74LS138 which would need 3 data bits to decode 8 outputs which could enable 1 of 8 banks to receive data. I'm also a little confused whith your description"My intention is to have output 1 send the data signal, and make that common to all the driver chips. Pins 2 through 7 will send a clock signal depending on which set of digits is to be updated, and Pin 8 will select between the A or B outputs..."Are you saying the data for all the segments, for all the displays, in all the banks is serial? And pins 2 thru 7 will select which of the 5 bank of displays you want to update?Gus B

"First of all, it's considered bad practice to not have base resistors on the transistors."This is purely a functional schematic to show what it is I'm looking for in a chip.... if I end up going the transistor route there'd have to be tweaks to a real layout, I know."Are you saying the data for all the segments, for all the displays, in all the banks is serial? And pins 2 thru 7 will select which of the 5 bank of displays you want to update?"Yes, that's correct. To update bank 1 the clock signal is sent on pin 2 with pin 8 held low, for bank 2 it's sent on pin 2 with pin 8 held high, for bank 3 it's pin 3 with 8 low, for bank 4 pin 3 with 8 high, and so on. With the data signal sent to all 12 banks via pin 1, that lets me drive 12 x 5-digit 7 segment displays (or a total of 420 individual LED's) with just 8 input pins from the pic.Richard

Hi Tuomas, I thought about using BCD - 7 seg drivers, but the problem is they're one per 7-seg, so for 12 five digit displays you need 60 chips. Using the M5451's cuts that down as each chip can handle a full five digit display itself. Converting the decimal input from FS to the serial data for the drivers is repetitive but easy, the Picaxe can do it just fine. In fact even something like a 16f84 could do it, which would remove the need for this 'output doubler' I'm looking for, but I have no experience in programming PICs directly. Picaxe basic I can handle :-)

Richard,Gus is right. This type of function is typically done with a decoder/demux. The '138 is a 3 to 8, and the '154 is a 4 to 16. (The '154 may be obsolete, however.)You can apply data and shift clock to all the M5451's and use the '138 to generate individual display register load signals. If you need more than 8 load signals, add another '138 using the same three inputs as the first. The '138 has enable inputs that can be controlled by a 4th PIC output that can act as a group select. Sounds like an interesting project. How are you interfacing to the PC? Serial, USB, parallel?Mikewww.mikesflightdeck.com

>Picaxe basic I can handle :-)If you can handle Basic, you can handle assembly. It's hard to beat assembly when you're working at gate-signal-level. You know exactly (more or less ;-) )what you'll get for outputs and when they will change. Once you get an interpreter or compiler in the loop you are subject to "clever things" that got coded into them.Mikewww.mikesflightdeck.com

I'm using serial to interface with the PC. I thought about USB, but the Picaxe doesn't handle HIDCOMM so I'd need another interface chip..... KISS!I have it working on breadboard already but just need to get the issue of showing more banks than I have outputs settled before I move to PCB.Richard

Hi Richard,looks like the M5451 clocks in the data bits at the postive transition of the clock line. So you might need the opposites of the '138 or '154 (these are inverting demuxes)... maybe the 74x238.Manuel

>Hi Tuomas, I thought about using BCD - 7 seg drivers, but the>problem is they're one per 7-seg, so for 12 five digit>displays you need 60 chips.Um, from the specs I understood one chip handles 8 digits, and you can chain them..? But I dont know my way around that deep into electronics really. Just remembered someone mentioning these.//Tuomas