That's how you would put them in the circuit. Don't forget the series resistor from the A and B inputs to the zener/whatever logic elements you elect to use. Izt for a 1n4733 (5.1v) is about 50 mA so you can get about half that with about 820 - 1k ohms. That should be plenty of current to make the zener regulate. If you do not have enough current, it may creep up higher than you want. If you went with 4000 series CMOS or a 555, you can run the logic element part of the circuit up to 15V. Bill -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Patrick Richards Sent: Tuesday, June 01, 2004 5:46 PM To: PICLIST@MITVMA.MIT.EDU Subject: Re: ] Sequential Logic Circuit - two inputs / one output I hadn't considered using zener diodes. I'm assuming I would connect the cathode to the A or B input and the anode to ground. Is there a problem with having such a difference between the input voltage and the zener voltage: 24V - 5V = 19V? -Pat -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of William Bross Sent: Tuesday, June 01, 2004 1:48 PM To: PICLIST@MITVMA.MIT.EDU Subject: Re: ] Sequential Logic Circuit - two inputs / one output Patrick, First, my preference would be to use zener diodes on the inputs. A resistive divider would not provide any protection from your 24VDC supply wandering up or down. Next, the easiest solution for the logic would be an 8 pin PIC -- at least that way I don't have to dig up an old logic manual for the FF pinouts and state tables ;) Also, since you are using a pushbutton for the A input, there will be lots of bouncing edges that should be cleaned up -- easy to do with a PIC. The output can be any type of transistor or FET output with a high enough V and I ratings. That's my quick answer. As soon as I clean up a few issues here I'll dig up my old logic manual and see about a FF type solution. Bill -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Patrick Richards Sent: Tuesday, June 01, 2004 2:16 PM To: PICLIST@MITVMA.MIT.EDU Subject: [EE:] Sequential Logic Circuit - two inputs / one output I am looking for help in designing what I am sure is a very simple sequential logic circuit. The circuit will have two inputs and one output. Lets say the inputs are A and B and the output is X. A and B will be at either 0VDC or +24VDC. I have +5VDC and +24VDC available to the circuit, so X can be high at either voltage, but I would prefer +5VDC. The initial state is A, B, and X are low. On the rising edge of A, X goes high. A is the output of a pushbutton switch. This could actually be rising-edge-triggered, or high-level-triggered. A will return to low. On the falling edge of B, X will go low. Here is simple diagram: |----| A----| |------------------ |----| B--------------| |-------- |--------------| X----| |-------- My main concern is to keep the circuit as simple as possible. I would prefer to do this with one or two logic chips and a few support components. I have ruled out the use of a PIC microcontroller because the person who will be using this circuit may need to build several of these over the next few years and I won't be available to program PICs for him. I have some thoughts on how to do this. I expect I could use some combination of flip-flops to latch on, then off. I could power the chip(s) using the +5VDC power supply I have available. To handle the 24V input I could use a voltage divider composed of a 10K resistor and a 2.2K resistor, with the 10K wired to the A or B inputs, the connection between the resistors wired to the input of the logic circuit, and the 2.2K resistor wired to ground. Any help would be greatly appreciated. Thanks, -Pat http://www.patrickrichards.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.