Feedback on 555 timer Schmidt Trigger design

Question

Can I get members insight into using a 555 timer as a schmidt-trigger design that I pulled from the Internet? 
 I found this schmidt-trigger design using a 555 timer. I would like to use it to condition the output of a photo-resistor. The 555 timer output will feed the input to a Arduino Mega. I'm in the process of bench testing the setup to finalize component values. While testing I figured I would throw it out to some more enlightened minds than mine for feedback. 
 I'm using the 555 only because I have a stock of them. I don't have any readily available smidth-trigger IC's so I figured I would go with what I have and build from scratch. Building from scratch especially using Internet designs comes with risk. I was hoping to mitigate the risk by getting community feedback. 
 If inquiring minds suggest you don't want to do this, that is a good thing.

AE7HD · Answer

I've used this circuit for remote capacitive sensing. It returns a pulse width proportional to capacitance between the sensor plate and ground. It is described here as a level sensor, but it also works as a body sensor, touch sensor, basically anything conductive that gets close will cause the pulse width to get longer. 
 https://hackaday.io/project/183506-remote-continuous-liquid-level-sensor-555-timer 
 To use: connect to one pin of an Arduino. 
 Now just time how long it stays high between low pulses. 
 The sensor should be two small copper plates or foil next to each other under the train, one connected to the sensor input, the other to circuit ground. Do NOT ground the sensor at the track, only back at the Arduino. 
 You'll just have to test it and see how sensitive it is in your case. Larger copper plates will be more sensitive. Make both plates the same size.

AE7HD · Answer

That should work. Remember, though, don't ground it to the track. The 555 circuit can sit right under the copper pieces, so there is very little wire to add parasitic capacitance.

Feedback on 555 timer Schmidt Trigger design

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