Making snail sensor independent of voltage

Thread Starter

Paramecium

Joined Jun 2, 2021
19
hi Para.
I am interested to know what a 5 sec operation of the motor is going to do, when triggered by a Snail.???
@Paramecium
E
Chop its head off, of course! This is for the Arion Vulgaris which is an invasive species here in Norway (and most of Europe). They are sometimess appearing at such numbers that they are driving people nuts.
 

Ian0

Joined Aug 7, 2020
2,718
Chop its head off, of course! This is for the Arion Vulgaris which is an invasive species here in Norway (and most of Europe). They are sometimess appearing at such numbers that they are driving people nuts.
A slug! I felt sorry for the snail, but not a slug (or “naked snail” as they were called in 17th Century England)
I’m now far more inclined to help, and might even make one myself if you get it working.
 

Ian0

Joined Aug 7, 2020
2,718
I'd give this a try:
Screenshot at 2021-06-03 20-03-33.pngUse a CMOS 555, and make sure that the MOSFET is fully enhanced at 2.5V
R4 and C3 help deal with the dip in battery voltage as the motor switches on.
S1 is the snail!
R1 should be about twice the snail resistance
 

djsfantasi

Joined Apr 11, 2010
7,772
Wait... to detect the snail, you have two copper areas close together.

When the snail creates a conductive path between these two traces, why not switch them from the sensor to a high voltage source to electrocute the snails?
 

click_here

Joined Sep 22, 2020
271
Wait... to detect the snail, you have two copper areas close together.

When the snail creates a conductive path between these two traces, why not switch them from the sensor to a high voltage source to electrocute the snails?
If you were going to do that, you might as well just have a higher dc voltage (say 4 x 9V batteries) and 2 copper traces.
 

Thread Starter

Paramecium

Joined Jun 2, 2021
19
I'd give this a try:
View attachment 240391Use a CMOS 555, and make sure that the MOSFET is fully enhanced at 2.5V
R4 and C3 help deal with the dip in battery voltage as the motor switches on.
S1 is the snail!
R1 should be about twice the snail resistance
Hmm. Thanks a lot. I did not think of the possibility that the motor was to blame for not triggering the 555 properly. Then I have something to investigate this week-end : )
 

Thread Starter

Paramecium

Joined Jun 2, 2021
19
If you were going to do that, you might as well just have a higher dc voltage (say 4 x 9V batteries) and 2 copper traces.
I haven’t tried, and haven’t found anything in the literature on this, but my hunch is that snail have a rather robust nervous system (relatively few, but big neurons). To kill them you would probably need to fry them, which cost a lot of energy (since they contain a lot of water).
 

Ian0

Joined Aug 7, 2020
2,718
I haven’t tried, and haven’t found anything in the literature on this, but my hunch is that snail have a rather robust nervous system (relatively few, but big neurons). To kill them you would probably need to fry them, which cost a lot of energy (since they contain a lot of water).
I had read that because they were fairly conductive (due to the slime) they would stop and go away if they encountered too much voltage. But if they only go away, they can come back later. . . .
 

click_here

Joined Sep 22, 2020
271
I had read that because they were fairly conductive (due to the slime) they would stop and go away if they encountered too much voltage. But if they only go away, they can come back later. . . .
At uni I was making a multi cell battery balancing circuit for my final year project.

I was working in my studio in my backyard and I can confirm that multiple snails walked across my pbc and fried - I had to move where I was charging the batteries.

They were 8 LiPo cells and they definately killed some snails!
 

Ian0

Joined Aug 7, 2020
2,718
I'm not sure what's going on here. Did you intend the op-amp to add gain? Or did you intend to use it as a comparator with hysteresis.
If the former, then the feedback is to the wrong input pin. If the latter then the upper hysteresis level is set at the positive supply, meaning that input has to exceed the positive supply to reset it, which it won't.

I'm not too sure what can be achieved by adding gain, nor why hysteresis would be required.
A 555 with a 2MΩ pull-up would detect a 1MΩ snail without any amplification. Adding a gain of 23 would be triggered by 23MΩ - a slightly humid day in a neighbouring country would set if off. But seriously, the slime from the first visitor would be enough to leave it permanently ON.

Also, I see the decoupling to prevent the voltage dip when the motor is switched on has been deleted. With added gain, the supply disturbance will become a worse problem.

There is more than one MOSFET with 30N06 in the part number. 3V won't switch a FQP30N06 on, but it will switch a FQP30N06L.
 

Thread Starter

Paramecium

Joined Jun 2, 2021
19
Actually, a snail just went in my trap and got killed. Not very impressive though as it was in a closed tube and had nowhere else to go. Unfortunately it made a great mess. Appearently half of the animal got through before the trap triggered. My intention was making it sensitive enough so that the tentacles triggers the action, and just the head goes off, making less mess and leaving the touch plate as clean as possible. Thats why I would like the system to react really fast. I have tried the 555 with megaOhm pullup, but it is not fast enough to be triggered by a very short tap with a finger. On the other hand, making it that sensitive will make it permanently activated with any small residues, as Ian0 pointed out.

Well, at least I now have more to tinker with. Thank all of you for your contributions.
 

click_here

Joined Sep 22, 2020
271
I think that a pull down between R1 and R3 to make it a comparitor would work better - You could add a trimpot and adjust your threshold

And it would be good if you could go find a slug, measure its resistance for a ball park figure

Have you thought about what you are going to do if it rains? If water gets on your sensor you will have one false reading after another
 

Thread Starter

Paramecium

Joined Jun 2, 2021
19
Yess, now it works! :)The trouble with the 555 was actually driving the mosfet. Everything worked fine on my scope without the mosfet. With the mosfet the timing got interrupted somehow, there was just a small motor jerk. A diode and a resistor to discharge the mosfet made the trick. Now it even works down to about 2.3 volts. Here is the circuit: Bilde_2021-06-05_101905.png
Thanks again for all your help and suggestions!
 

Ian0

Joined Aug 7, 2020
2,718
Seems dubious to me. On a 2.3V supply the diode will limit the gate voltage to 1.8V which is hardly enough to switch even a logic-level MOSFET.
Probably it's limiting the motor current and thus preventing the supply dipping as the motor starts.
 

ericgibbs

Joined Jan 29, 2010
13,277
hi Para,
Why are you using a 3V battery, which is requiring additional circuitry in order to make the project work,
a 4,5V or a 6V battery would be a better choice.
If its a 3v motor, use either a 3V battery for the motor.

E
 
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