Instructables
Many of the citizen scientists all around the world might have faced this problem that thier sunflower or any other plant is eaten up by critters before it even fully grows , so I have come up with a very simple solution to this problem , expose the critters to high frequency noise which they wouldent be able to tolereate and will not get near your plant .

This critter repellant is basically a high frequency emmiter ( 61 Khz ) based on the 555 timer . The 555 Timer is a powerful chip for low cost projects by adjusting the values of components that you will be connecting to it you can make it emit various frequencies . The Timer in our circuit will function in astable mode which will put out a continious stream of stream of rectangular pulses having a specified frequency. 

This instructable will explain some basics on how it works , the parts needed , how to prototype the circuit on a breadboard , and finally soldering everything into place.
 
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Step 1: Parts & Tools

Picture of Parts & Tools
Parts :
~ LM555 Timer - Mouser Electronics 
~ 10 k Ohm Resistor - Mouser Electronics
~ 6.8 k Ohm Resistor - Mouser Electronics
~ 1nf Ceramic Capacitor - Mouser Electronics
~ 1 uf Ceramic Capacitor - Mouser Electronics
~ Piezo Speaker - Local Electronic Store
~ 9v Battery - Local Electronic Store
~ 8 Pin DIL Socket - Local Electronic Store
~ 9v Battery Snap - Local Electronic Store

Tools :
~ Soldering Iron - Mouser Electronics
~ Solder Wire Lead Free - Mouser Electronics
~ BreadBoard - Mouser Electronics
~ ProtoBoard - Mouser Electronics
~ Single Strand Wires ( Used As Jumpers ) - Mouser Electronics

NOTE : Use A High Frequency Piezo Speaker Which Can Handle A Frequency Of 65Khz

The Price Of All The Parts Before Shipping Is 5 $ . Assuming That You Have All The Tools Already On Hand.

Dave Kruschke8 months ago

Hello,

In your instructable here you reference another site that allows one to calculate frequency given two resistors and one capacitor. This site also reveals the correct, workable schematic for your device. But both your schematic and your "Fritzing" show the 10k resistor at point X (on my schematic below) going to 0V instead of 9V as also shown on the other site you referenced. The device built using the schematic below oscillated at a measured 61 kHz using a variable resistor (pot) set to 5.9k (rather than 6.8k as shown in the schematic) - a very minor difference. But again, the 10k resistor must go to +9V not -9V.

I'm a little surprised that you measured 65536 as shown on your Instructable as 65536 is exactly 2 raised to the 16th power.

The tip of your soldering iron in your picture looks way, way too blunt to solder up a proto board. I always file my soldering iron tips to a sharp, tapered point, even if doing this shortens the life of the tip.

Finally, and perhaps least important, is the fact that ultrasonic devices have been shown in the US to not work at all for deterring mosquitoes. The wings of the female mosquito vibrate at about 400 Hz while the male mosquito wings vibrate at about 600 Hz. Both mosquitoes listen in for each other at around 1200 Hz, the third harmonic for the female and the second harmonic for the male. These mosquitoes don't listen to any ultrasonic frequencies produced by bats and this is why these device don't repel mosquitoes. And the large wings of the dreaded dragon fly vibrate at a much lower frequency than the female mosquito and are not known to be heard by mosquitoes...

Dave Kruschke

555 schematic corrected.jpg

PS; Please click on the above schematic to see the full schematic!

PS, again, some additional comments:

First, a simpler 555 device with fewer parts
is presented here - see schematic below. Notice how the frequency changes with
the battery voltage? Not a horrible problem but something to keep in mind. In
fact, a decreasing voltage that causes a decreasing frequency might offset any
possible "notch effect" raised by another reviewer here.

For my device, I deliberately used common part
values for the resistor and the capacitors. The purpose of using the larger
capacitor is to be able to test the circuit when desired as the device makes an
audible sound to humans when the larger capacitor is used. This capacitor could
be used with a switch to "switch in" to test for an audible sound,
indicating that "all is well" with the device.

When I went on and on about mosquitoes, I
falsely assumed that mosquitoes were being target here. But now I am aware that
other animals (rodents, perhaps) were being target such as those that eat crops
intended for people. I looked up some hearing frequencies for various creatures
and found:

Humans; 20 Hz to 20 kHz, Cats; 55 Hz to 79
kHz, Dogs; 40 Hz to 44 kHz, Bats (ugh); 15 kHz to 90 kHz (typical), mice; 1 kHz
to 70 kHz (baby mouse in distress = 40 kHz) and finally Birds of the Aire; 1
kHz to 4 kHz plus.

If anyone deploys one of these 555 devices
amongst crops, it would be interesting for sure to see what the effective
radius is (if any)....

Dave Kruschke

555 simplest.jpg
Hadmahon1 year ago
I like this idea! Anyway, the first thought that came to my head was: Could it harm bats somehow? That wouldn't be exactly cool.

I wouldn't lose any sleep over bats. In the Northern US, one out of every 100 bats carries rabies and people that get it die a horrible death. So I am not sympathetic to those that harbour bats because they think they are cute or "beneficial."

Fishing Dr Morgan.jpg
Bot1398 (author)  Hadmahon1 year ago
This Device Wouldent harm any any animal in any way it will just keep it away from the place where you keep the device
Raphango1 year ago
Great project!
Congratulations!
f23647381 year ago
the cuircuit image file for the yEd software (my post below)is at http://www1.datafilehost.com/d/d3636286
if i have made a mistake please correct it.
f23647381 year ago
http://www.picvalley.net/u/1900/39262872517610507601371356530eRqAtakeNHCaslotmWAr.PNG
more info http://puppylinux.info/topic/yed-flow-charting-made-easy?replies=7#post-5790

variable resistor from 1-10k ohms please. she says no have. can we have an image of this beast please. what is an audible frequency and corresponding ohm resister to test the speaker? more info on the piezo speaker would be nice as this is also proving hard to get. PS i am in the third world.
pyrohaz1 year ago
Brilliant instructable! Voted, also on the VFO thing, you could do that using two 555 timers, something like: http://www.555-timer-circuits.com/police-siren.html

Instead of having the 10k resistor from pin 3 though, take it from pin2 and the frequency will vary between a high and a low point (dependant on the value of control voltage) if you make the 10uF capacitor on the left timer really large like 1000uF, the sweep will take much longer to do.

Still! Awesome instructable :D
J-Five1 year ago
I agree Genuis, and on the last page was that Spongebob?
Bot1398 (author)  J-Five1 year ago
No , Its Not exactly a spongbob I got that image somwhere on google images and then I edited it
J-Five Bot13981 year ago
But still it's good use of electronics
dc-labs1 year ago
Great stuff!

I know this works based on personal experience.

When I was a lad I used to experiment with 555's making audio frequency oscillators. One time I had a tweeter attached and was sweeping the frequency range. I didn't realize until the frequency went really high that there was a mouse behind my bookshelf. When I swept the high-end, the mouse was clearly agitated. I could hear it scrambling, trying to climb up the back of my bookshelf. The sound was driving it nuts!

My understanding is that rodents will develop "notch hearing" if the frequency is kept the same. Any ideas on creating a VFO for this design so as to automatically sweep the frequency?

Bot1398 (author)  dc-labs1 year ago
To change the frequency you can replace 6.8k Ohm resistor with a Variable resistor . You would have to rotate the knob every few days and it will not be automatic .
Genius.