I did this for a project last year. I was instructed NO Micro Processors! They took all the joy out of it! I hope this helps and I can remember what I did. You have to allow for the following: 1) De-bounce switches using RC. I also used a Schmitt Inverter following each switch. 2) Consider pushing more than ONE button, I made the circuit ignore that condition. 3) Consider power up (RESET) conditions, what switch do you want selected when power is turned ON, if any? This is probably the hardest part of the project. 4) Do you want active HI or LO latch outputs to run your application? I designed a heater control panel for a medical product with the following: 1) I de-bounced the push-button switches (active low) with a large RC (10K & 10uF) and ran them through a Schmitt triggered inverter (1/6 of74HC14). My switches pulled a large (10uF) de-bounce capacitor to ground, so I used a 100 ohm resistor in series with the switch to limit current. 2) Run the conditioned switch signals (4 in your case) to a 1 of 10 decoder, a 74HC42. This will decode all switch combinations. Choose outputs from this part that are only for desired input. The 1, 2, 4 or 8, the others decode more than one key-pressed. 3) Run these select signals to a Quad Latch 74HC75, Data inputs. Add some delay on them (RC) so the signal doesn't go away before the Latch/Clear signal goes Hi. I used 100 ohms and .01uF. This was a gate propagation race! Choose active Hi or Lo outputs from the 74HC75. Buffer them well, if going out to nasty stuff! 4) Make a Latch/Clear signal for the 74HC75 by "ORing" the active Hi signals from the 74HC14 inverters. When any switch signal goes Hi (switch pushed), the latch outputs are cleared. When all switches are let up, the data is latched. Remember to add the delay mentioned above. 5) A Power ON reset circuit needs to be "Ored" into this latch circuit. I used 2 or 3 input NOR gates here (74HC02 or 74HC27) for "ORing" and a section of a 74HC14 with RC for this. If all fails, reach for Don Lancaster's CMOS Cookbook! Good Luck! Mike Hagen -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use mailto:listserv@mitvma.mit.edu?body=SET%20PICList%20DIGEST