Guest lightnix Posted May 31, 2003 Share Posted May 31, 2003 I am currently getting a small project together, which requires a pair of ultra bright, white LEDs to be switched on and off via a single, momentary action "tactile switch", of the kind used in mobile 'phone keyboards. Unfortunately they don't seem to come in latching on/off versions, so an electronic solution is required, involving some kind of "simple" (transistor ?) latching circuit that doesn't involve big, chunky relays. Does anybody know of one that I could build ? I can probably work out the construction from a circuit diagram without too much difficulty. All offers of help will be gratefully received and the provider of the best solution wins a pint (or two !) at the Blue Room Get Together in June or at PLASA (date tbc). Thanks in advance. Link to comment Share on other sites More sharing options...
Ketil B Posted May 31, 2003 Share Posted May 31, 2003 Hi the thing I can think of is a JK Flip-Flop. If you hold the J and K inputs high by tying them to the +ve supply and connect the switch to the clock input then the out put will toggle(remember that they have to outputs one is the inverse of the other). the output amps will not be much 0.4 mA for TTL chips and 4 mA for CMOS chips (these values are what I remember of the top of my head, so don't quote me) so use an op-amp to get the output to the right volts and amps. Hope this helps :D Link to comment Share on other sites More sharing options...
kalmatthew Posted May 31, 2003 Share Posted May 31, 2003 You could use a JK type to make a D type flip flop if you are prepared to wait abit a can provide a circuit diagram. However this will have to be late june some time as I have GCSE's at the mo PM me if ur intrested Link to comment Share on other sites More sharing options...
Peter Tovey Posted June 1, 2003 Share Posted June 1, 2003 You could use a JK type to make a D type flip flopWhy - a JK bistable is exactly the right answer for this, and a D type latch isn't (sorry). As Ketil says, then attach the Q output to a non-inverting op-amp circuit with the two resistors chosen to give an appropriate DC gain, and you're flying. Clock input for a JK can be something as simple as a doorbell type switch (or what you suggest). Details in any decent book on digital circuits. Peter Link to comment Share on other sites More sharing options...
themadhippy Posted June 1, 2003 Share Posted June 1, 2003 something complecated like this?http://homepage.ntlworld.com/themadhippy/dtype.jpgI do belive its a d type flip flop,used a simlar circuit for a basic call lights system,also can be used as a dived by 2 thingy. or would something simple like a self holding relay do the job ? Link to comment Share on other sites More sharing options...
Brian Posted June 1, 2003 Share Posted June 1, 2003 except that with the above circuit you'll never guarantee whether the LED will end up on or off. You'll need to debounce the switch otherwise you will get an indeterminate number of clock pulses. Link to comment Share on other sites More sharing options...
themadhippy Posted June 1, 2003 Share Posted June 1, 2003 You'll need to debounce the switch otherwise you will get an indeterminate number of clock pulsestrue,but at 4 in the morning after an amdram get out, do you expect me to even rember what day it is :D Link to comment Share on other sites More sharing options...
kalmatthew Posted June 1, 2003 Share Posted June 1, 2003 I need to correct my mistakes it was 1 in the morning and I had been drinking. I menat a T type flip flop as suggested previously. http://216.40.249.192/s/contrib/corky/smilies3.gif. This is how I would do it Link to comment Share on other sites More sharing options...
Brian Posted June 1, 2003 Share Posted June 1, 2003 can I be picky again? It's not considered good practice to run LEDs from the output of a logic gate to ground, better to go to +ve. Your circuit will still work if you 'flip' the LEDs but the outputs of the logic will thank you. Brian who hasn't had a drink (yet). Link to comment Share on other sites More sharing options...
Brian Posted June 2, 2003 Share Posted June 2, 2003 Having just re-read the OP I note that he wanted to use transistors and, more importantly, was offering beer for the best one. My I humbly submit my first entry...My Entry Link to comment Share on other sites More sharing options...
kalmatthew Posted June 2, 2003 Share Posted June 2, 2003 Umm can I just chek on wether ur switch is push to make or wether it is spdt or spst. Also I belive Brian if you read it you will find that he just sugeste the use of a transistor and with a relay can hardley be called chunkey. Matthew Link to comment Share on other sites More sharing options...
Brian Posted June 2, 2003 Share Posted June 2, 2003 The switch is a momentary action normally open jobbie (jobby ?). To prove my idea worked I've actually built one. It's a transistor version of a chip version I use all over the place. The chip version needs just two inverters. and I think the original request was... >Unfortunately they don't seem to come in latching on/off versions, so an electronic solution is required, >involving some kind of "simple" (transistor ?) latching circuit that doesn't involve big, chunky relays. Brian who really must get a signature set up. Link to comment Share on other sites More sharing options...
Ketil B Posted June 3, 2003 Share Posted June 3, 2003 It's a transistor version of a chip version I use all over the place.can you give a number for the chip? just interested :D Link to comment Share on other sites More sharing options...
Brian Posted June 3, 2003 Share Posted June 3, 2003 Most any spare inverters you've got lying around, it works best with CMOS. Try a HEF4069, six inverters in a package = 3 push-button circuits. It looks like this... Chip-Flop Output(s) can be taken from either/both gates. Brian Link to comment Share on other sites More sharing options...
nick Posted June 9, 2003 Share Posted June 9, 2003 A Simple Thyristor will do the same job, only snag is the power would have to be momentary cut to unlatch after. Link to comment Share on other sites More sharing options...
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