??? 08/11/04 02:27 Read: times |
#75713 - RE: READY FOR SCHEMATICS Responding to: ???'s previous message |
For the row address decoder I would use 74HC238 and one of its negative enable inputs directly connected to micro. 74HC238 drives ULN2003 with 330Ohm collector resistors. ULN2003 drives seven BD676 via 220Ohm base resistors. This forms a rather fast LED driver array, well suited for this multiplexing application.
For the shift registers I wouldn't use 74ALS164, because they don't contain output registers. 74HC595 is a better choice. Internal output regsister allows to display actual row, while the next row is loaded into the shift registers. But to benefit from these output registers an additional signal must be routed to them, the signal by which row data is transfered to output registers. So, for 74HC595 you would need three signals: 'Data', 'Clock' and 'Store'. These 74HC595 then drive ULN2003, which are capable to sink the LED currents. Kai |