Post by thread:Multiplexing and 7 seg LEDs

Folks a couple of days ago there was a thread re multiplexing 7 seg leds from 16F84. Has anyone considered the M5450 LED drivers. Serial in (only 2 PIC pins!!!) and 34 parallel out. Designed specifically for driving 4*7 seg LEDs but output can sink 15mW so might be useful as a general port expander. Will run at clock speeds up to 0.5Mhz which should be OK for many applications. Looks simple to program, clock start bit, 4*8 data bits (7 seg +dp), 2 extra bits (for centre colon on clock displays). 36th clock high loads the shift registers into their latches, next clock low generates reset. Farnell (at least) stock them. Farnell and Radio Spares also stock complete 4* 7 seg LED modules from Three Five systems that have the drivers built in. Haven't tried this yet but hope to get chance this w'end. Brian Brian E Jones Centre for Java Technology IBM HURSLEY

I have used the 5450 - it is as easy to use as it seems. The only gotcha's are ensuring the correct number of clock pulses per cycle so it doesn't get lost. Driving from PICBASIC (!) takes only a few lines of code. Display brightness controllable. No segment resistors needed. Very few other parts needed - a few r's and c's. Good drive current (15ma? per pin) (sink only). An oldie but a goodie. Russell McMahon From: Brian Jones <spam_OUTbejonesTakeThisOuTHURSLEY.IBM.COM> a couple of days ago there was a thread re multiplexing 7 seg leds from 16F84. Has anyone considered the M5450 LED drivers. Serial in (only 2 PIC pins!!!) and 34 parallel out. Designed specifically for driving 4*7 seg LEDs but output can sink 15mW so might be useful as a general port expander. Will run at clock speeds up to 0.5Mhz which should be OK for many applications. Looks simple to program, clock start bit, 4*8 data bits (7 seg +dp), 2 extra bits (for centre colon on clock displays). 36th clock high loads the shift registers into their latches, next clock low generates reset.

At 09:38 03/05/99 +1300, Russell McMahon wrote: >I have used the 5450 - it is as easy to use as it seems. >The only gotcha's are ensuring the correct number of clock pulses per >cycle so it doesn't get lost. is there a way to set it into a defined state if it gets lost? ge

The book suggests yes but I recall having some problems with this early on (some years ago). (Something like sending a single data bit followed by more than a complete set of clock bits. The IC starts the frame at the first data bit and then clocks through one frame and stops until another clocked in high is received. I don't know if my original problems were my programming or a failure of the IC to match claimed specs (the former seems more likely :-)). In practice it seems very well behaved when driven as intended. Russell McMahon . From: Gerhard Fiedler <.....listsKILLspam@spam@HOME.COM> >>I have used the 5450 - it is as easy to use as it seems. >>The only gotcha's are ensuring the correct number of clock pulses per >>cycle so it doesn't get lost. > >is there a way to set it into a defined state if it gets lost? > >ge >

Hi - I have (tried the Farnell thing). It works like a charm - Also on the smaller '508. Holger {Quote hidden}> ---------- > From: Brian Jones[SMTP:bejonesKILLspamHURSLEY.IBM.COM] > Sent: Thursday, March 04, 1999 11:04 AM > To: .....PICLISTKILLspam.....MITVMA.MIT.EDU > Subject: Multiplexing and 7 seg LEDs > > Folks > a couple of days ago there was a thread re multiplexing 7 > seg leds from 16F84. Has anyone considered the M5450 LED > drivers. Serial in (only 2 PIC pins!!!) and 34 parallel out. Designed > specifically for driving 4*7 seg LEDs but output can sink 15mW so > might be useful as a general port expander. Will run at clock > speeds up to 0.5Mhz which should be OK for many applications. > Looks simple to program, clock start bit, 4*8 data bits (7 seg +dp), > 2 extra bits (for centre colon on clock displays). 36th clock high > loads the shift registers into their latches, next clock low generates > reset. > > Farnell (at least) stock them. > > Farnell and Radio Spares also stock complete 4* 7 seg LED > modules from Three Five systems that have the drivers built in. > > Haven't tried this yet but hope to get chance this w'end. > > Brian > Brian E Jones > Centre for Java Technology > IBM HURSLEY >