volk

Greetings,

I have a question about latches. I want to make a circuit that does the following: After I turn it on, one of the switches is ON, until I press one of the buttons. After the first button the switch stays OFF, even if I press that SAME button again. I'm using the CD74HC4066E switch.

I was thinking of using a latch to solve the problem, but I just can't figure it out. If anyone has a bright idea, please let me know.

ericgibbs

hi,
The 4066 is an analog/digital quad bilateral switch, what are you trying 'switch'.?

Your description is difficult to follow, can you repost with more details.

A simple block diagram is always helpful.

Like to help.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
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volk

Hi

Ok, here is the scheme diagram. The datalogger is connected to a keypad, and at PC startup, the send/receive lines must both be open, so that the PC recognizes the datalogger. The problem is that the PC communicates with the datalogger at all times, but all I want is to send limited information from the datalogger to PC - when I press the button on the keypad.

I successfully interrupted the datachannel (second picture) but now I must hold one of the keypad buttons at PC startup, to keep the channel open. The PC and the datalogger start communicating abter the first set of commands is sent from the datalogger to the PC - when I press the first button on the keypad.

I hope this helps.

Attached Images

	SCHEME1.jpg (16.1 KB, 11 views)
	SCHEME2.jpg (12.8 KB, 8 views)

ericgibbs

hi,
Get the datasheet for the HEF4053, Triple 2 channel analog /mux/demux ic.

This will enable you to select between the keyboard and logger to the PC.

You could use a simple mechanical switch to select KB or DL inputs to the PC or a 4013 D type F/F or a 4093 wired as a latch, which controls the 4053 select line.

If you are selecting by the 4053, the RS232 after the MAX232 level shifter you must have a dual supply to the 4053.

Is the keyboard output/input RS232 voltage levels. ? if not you may have to use a level shifter as the standard PC's RS232 lines swing about +/-12V [ it could be anywhere between +/-5V and +/-15V for a PC.

Does this help.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/