Hey, Am currently in the planning stage of my new mod (wahay!), and want to replace all the switches with touch sensitive ones From reading various threads, I get the impression that I need Active LOW for the mobo, and Active HIGH for CDROM switches. Can someone explain exactly which switches I'd need for what purpose? Is it what I stated above? How would I know which I needed? As well as this, Farnell only seem to do the QT110-D which is Active LOW. IIRC (from A level physics), that I could use a NOT gate to invert the circuit, but I haven't seen mention of NOT gates on these forums, which makes me suspect that NOT gates aren't what I need. I'm guessing a transistor or something, unfortunately, we don't do transistors in this sylabbus, so I'm not too hot on what they do etc. From what I can see, for the mobo, all I need to do, is use the sample circuit diagram in the other thread floating near the top of this forum, and connect the OUT pin to the ground pin of the mobo FPIO switch? What about for the CDrom etc? Thanks Ben
It's no good connecting it to the ground pin of the motherboard header, because that's connected to ground, you use the other pin. An Inverter (NOT logic gate) will do exactly what you need, or you can just use the appropriate QT110 IC variant to give active-high or active low, whatever you need, and you don't need extra components except for the QT110's normal capacitor or two. The reason transistors are sometimes used is because it's kinda wasteful to use a 14-pin 6-inverter IC when you just need one. The function is the same. Mobo's generally need active low, but i don't know about CD drives.
I can't get hold of the active-high QT110's, so I'll just buy a load of QT110s Active Lows, and an inverter. Would this one be ok?
What you've linked looks like a special single-gate 5 pin surface mount package, which just has 1 gate in it. That will work, but i would have thought that a more common chip such as the ordinary 74LS04 or 4069 would be cheaper and easier to get,
Perfect. You could use the first chip you linked, but you'd need to know the pinout and it would be harder to solder.
Just remember that the QT110 output has a maximum of 4mA, so I'd recommend not using the switch/inverter to power anything, but rather to throw a transistor, relay, or optoisolator to activate stuff from another power source. Also, if you're going to use multiple QT110s you should probably just go for the QT140. It's basically 4 QT110s in a single chip, with circuitry to keep the individual sensors from interfering with each other. The thread on the circuits I'm working on using the QT140s (and evolution of the concept) is over here: Touch Control Panel. Final schematics of what I came up with are on the third page.
It depends where he's located, but in some parts of the world these things are hard to get, and the single QT110x is the easiest to find.
He's in Oxford, UK according to his profile. Farnell sells them and has them in stock available to mail order. Farnell, UK just search for QT140.
Thanks techno, I like the look of that circuit! One question - what does all the stuff from OUT1 do? Is all that just to turn on/off the internal lighting?! Edit: Just read the thread properly... You're having two QT140s - one to light the LED on close prox, and the other to actually activate the circuit? Good luck! I like the continous power on LED idea!
The problem with Farnell is their £20 min order. And free delivery only applies to orders over £30, otherwise there's an extra £3.52. If you can't find enough bits to make that amount up, Futurelec have the QT110 and will ship to the UK for $3, under £2.
Yup, it's a flip-flop circuit tied to the OUT1 (slightly modified from cpemma's schematic). The other option was to use a seperate QT110 in toggle mode. On the QT140 all switches need to be in the same mode, and most of the stuff needs momentary contact (power switch, etc). Hehe yeah, I'm hoping it works. It should, but we shall see. You mean actually having the power switch illuminate on proximity even if the system is off? It's kind of necessary as the switches will be behind a tinted plexi plate, and I don't want to have to poke randomly at the plate looking for the switch to turn the machine on
Interesting idea. The price difference between a QT110 and QT140 at Farnell is only 50p for the 140, and 65p for the 150. Half tempting to get a bunch of 150's for flexibility especially as I only need to connect a cap aross the unused sensors. ooh right, so its not continously on, rather still proximity even when its off? Nice!
