You always need either a localised ground physically close to the sense electrode (for floating battery powered operation) or a good connection to real earth, although this can generally be supplied capacitively even through an isolation transformer or wall power supply with an isolated earth. By the way - grounding is very important in capacitive sensing solutions, proximity or otherwise. If this is not the case then an optoisolator is certainly one useful solution to getting a signal out. With that in mind - answers to your questions:ġ) There should be no issue in connecting the output of the 555 to another high impedance input provided the two circuits share a common ground. To my mind the learning opportunities with these are far greater too, as you can see the effect of changing a wider variety of operating parameters. Others will require a microcontroller, but generally allow much more adjustability and tweaking. Some will be useable without a microcontroller to configure them and interpret readings. Each will have their own benefits and downsides. Take a look at breakout boards available from companies such as Adafruit and Sparkfun for easy-to-use solutions. Although some microcontroller manufacturers implement elements of this in their products, none do it so well as the dedicated ICs. They implement sophisticated baseline filtering to allow for long-term environmental drift, use advanced detection algorithms and have dedicated onboard hardware to generate drive signals for the electrode - none of which have to be implemented in software. I would strongly recommend using a dedicated capacitive sensing IC for anything other than very simple touch buttons. However, you will not learn a huge amount doing so, and neither will the end result be a system that is robust to environmental changes - for example long-term drift in humidity. you would be able to get the circuit to do what you want. I'm certain that with enough careful design of the physical sensor electrode layout, tweaking of component values etc. It is very handy, but there is a near-fetishisation of trying to achieve things with the 555 which, although possible, are certainly not optimal solutions. The 555 is a general purpose timer which has been used to implement a wide variety of other circuits over time.
I am surprised that the circuit stopped working when you added an LED, but that is likely something of an aside in the context of this question. There are so many capacitive sensors design out there, so I chose what seemed simple. But for sure there will be two sensors used.
Something ON/OFF or whether MCU will be required for more advanced logic. I have not yet decided whether the sensor output will just plainly switch Is some kind of oscillator needed after all?Ģ) Is it possible to turn this into proximity sensor (1 cm distance is enough) or does it make sense to go with ICs like QT113 and the like? Will proximity work outside, where there is no low-freq electric lines noise? To be honest, when the plate is connected to the ground, touching R1's open end has the same effect, which is reasonable as the body makes a capacitor with the plate.ġ) Does this design have any problems if the logic output will be connected to some other circuit? Should I use optocouplers for instance to prevent noise? update: one problem I found after writing this is that when I switch off the table top lamp, the sensor works no more. Except for I needed to touch the ground T0 to activate.
(Needless to say, the circuit is not connected to anything, works on battery, build on a breadboard) But then the thing worked even better as touch sensor. Then I decide to try with a led (without the 'scope), and the proximity sensing was there no more. And, wow! the plate worked most of the time as a proximity sensor.
Q1 hFE is over 300, if that matters.Īt first, I checked with a 'scope at the Q1 collector and 8k resistor instead of led and smaller resistor. Sorry for the odd-looking schematics: gschem usability is near zero. I've found one simple schematics for capacitive sensor on, and implemented it as follows:
0 kommentar(er)
