The Undesirable Visitor (VENT006E)

There is a limit for pranks, and when the electronics comes into the game, the results can be very interesting. See how Bart and Bert, with the help of Professor Ventura, get rid of an unwanted visitor with a simple electronic circuit. In this story, the reader will have elements to assemble a simple circuit capable of disturbing his/her friends, without hurting anyone, in a very interesting game.

This story is from the 1990s and has not been published yet. Another adventure, which used a technology of that time and can still be used on technical education. The cricket and the dripper, for example, can be easily taught to high school and technical students as an excellent didactic project and with the purpose of a good prank, as in the text. (*)


(*) ART296E will show you how to mount the electgronic cricked used in this history. See more at the end of the history.


Skeeter was an annoying guy, and when a Bart’s mother announced that he would come and spend a few days at their home in Lemon city, both Bart and his cousin, just like Bert, his friend, who already knew him, twisted their noses!


- Crap! We're going to have to "put up" with that jerk’s jokes! - Bart whispered to his friend, so that his mother would not hear.


- I don’t think so! - Bert replied - we are prepared!


- How come?


- What is the “weapon” we’ve got which he doesn’t? - Bert asked mimicking a gun with his hand, where the index finger was the barrel.


- Of course! Electronics!


The other confirmed, and went on:


-And who can help us?


Imitating a hero from TV, the two spoke at the same time:


- Professor Ventura!


- So how do you want to get rid of the plague? - Professor Ventura attended his two students and friends.


- It must be something harmless, but it must disturb the jerk to the point of making him leave or at least preventing him from saying his foolish jokes! - Bart explained to Professor Ventura, who was quietly listening, but was already thinking of a solution.


When Professor Ventura, after some time, presented the project to Bart and Bert, the two of them said cheering:


- It's simple, cheap and it seems to work! Let's assemble!


The small appliances fit on the palm of a hand, and the performance tests weren’t hard. They worked!


Skeeter arrived a couple of days later, with his usual naughtiness! Shaking Bart's hand, at the Lemon city bus station, he already had a good time giving a "shock" on his cousin! He was wearing a small vibrator on his hand, the type acquired in a "magic house"!


Bart trembled, and Skeeter laughed heartily!


Seeing that, Bert commented:


- Argh! It will be hard!


Bart replied:


- This guy must have bought half the stock of "tricks" from the "magic house" and wants to use everything on us! He is so screwed! Wait and see!


The day was quite long for Bart and Bert, as Skeeter, the cousin, was a really "boring guy," because he did not know when it was time to stop with his pranks, doing one after the other, on Bart and Bert.


- Gotcha! Ha! - He would laugh


After smelly little stripes, dyeing candy, thumbtacks on the chairs, splashes of water without the nose, finally it was time for everyone to go to bed.


Bert was already leaving to go to his house when Bart stopped him:


- No! You have to help me! After all this, I’m sure you will want to see our "anti-annoying" gadgets in operation!


- I knew you wouldn’t let me miss the best part of the "party". I’ll just call home to say I’ll be staying here tonight!


But what were Bart and Bert really planning to "avenge" from the boring pranks?


Professor Ventura’s idea were simple: first the "dripper".


- Dripper! What the hell is that? Are we going to "extract" drop by drop of his blood?


The professor calmed him, although if it was that, the boy might even like it:


- That's not it!


Going to the blackboard, as he always did to present his project, Professor Ventura told them to settle down:


- Here it is! This is a dual-T oscillator, a configuration well known by you.


- There is no doubt, it generates a "good" sinusoid and also damped oscillations! ... - the professor interrupted Bart at this moment:


- Ah! There it is: damped oscillations! You know these oscillations are just like the ones we have when we hit some object, and it emits a sound for a while, right?


- Yeah! - Bert answered - They are like "percussions" which happen in many musical instruments! - after the boy showed he knew, the professor continued:


- See that we have two cases of oscillations to consider if the oscillations damp quickly, that is, they lose their intensity, we have dry beats like blocks of wood beating one another, or tambourine! Right?


- Right!


- But if the oscillations are prolonged with a more metallic sound, like a triangle, a bell, a marimba or a bass drum! ... - the professor gave more examples, but Bart "taking" the idea interrupted:


- Like a "drop of water"!


- Exactly! Said the Professor, pointing to Bart! - The disturbing drip of a drip! Like a Russian torture session!


- Wow! And, this is easy to assemble!


- Too easy, so let's "sophisticate" our project! - the Professor, using his experience started drawing the complete diagram of the device, and as he did so, he explained:


- The "heart" of the design is a dual T oscillator, around BC548, which we will adjust to produce damped oscillations in the frequency of a drop of water, between 3 000 Hz and 5 000 Hz. Capacitors and resistors must keep a 2 to 1 reason that you know well! Then, to drive this oscillator we use an astable with the known 555, which will give the "rhythm" of the drops. There is no need to talk about how this block works, because you know it very well!


- You can go on! - Bart reassured him and the Professor continued:


- Now comes the first "sophistication": let's put an LDR at the control input of the 555 so that the circuit only works in the dark! ...


- Why? - Bert did not "get" the motive, but Bart did!


- Of course! The "thing" will then "drip" when the light are turned off! We install it in the room and it will drive him "crazy"! When he turns off the lights “it" will drip! When he turns the lights on to see where the noise comes from, the "it" will stop! ...


- Great! - Bert agreed, now that he understood the prank! ...


- But wait, I'm not done! - the Professor had more to say, so he continued. - We still have to reproduce the signal. I'm going to use a very simple amplifier stage, with just one transistor and a small speaker! ... - Bert interrupted at this moment:


- Why not a good amplifier and a big speaker, to bother for real?

The professor made a negative signal with his finger:


- No! A loud sound would show that the dripping is artificial! We have to keep the actual volume with which a drop of water falls, so that he doesn’t suspect that something is artificial. A loud volume spoils everything, and he would find out right away!


- Ahh! - Bert exclaimed understanding better the "spirit of the thing"!


- Wow! This is going to be good, but what about the other project?

Professor Ventura continued:


- In order to keep him believing we change the device on the next day for a cricket!


- A cricket!


- Yes! People from big cities are not used to insect noises, it “bugs” them easily! For us, from the countryside, it’s different. It’s actually very pleasant at night, and helps us to sleep!


- A cricket inside the pesky guy’s room will drive him crazy! But how could we make it "sing" at the right time?


- An electronic cricket sings! You can be sure of that - The Professor said - And here's the project!


Again, picking up the chalk he went on to the second diagram. The first one had already been copied by Bart, who would assemble it:


- A 4093 perfectly suits what we want: let's use three of the four NAND ports as oscillators. The first gives us the sharp tone of the cricket’s singing, oscillating between 4 000 and 6000 Hz. This tone, to be just like the insect, is modulated with a sign of 4 to 5 Hz by an oscillator with another port. These two oscillators have a 50% active cycle. To have the intermittence we use a third port that will have an active cycle of 20%. This way, the cricket sings, let’s say 1 second and stops for 4 seconds. It will be a "boring sleep"!


- But what about the fourth door of the 4093, is it no good?


- Yes, it is! It amplifies the final signal by applying a small speaker through the transistor - The Professor explained.


- Is it also worth to use the low volume idea to be more realistic? - Bert had already "caught" the joke.


- Yes, exactly! But there is more: the circuit will also be triggered by an LDR, and so will work when the lights go out! ...


- Wow!


The two circuits were installed in small plastic boxes, with holes for the LDRs and small speakers, plus a switch to turn them off and on.


In the room where Skeeter was supposed to stay, Bart and Bert took care to choose a place that would allow a perfect functioning of the devices: on the wardrobe, during the day or with the lights on, the LDR would receive a reasonable amount of light and, with the sensitivity adjustment, the devices would remain inactive.


However, at night with a dim light, the circuits would came into action and the characteristic noise of dripping, or the singing of a cricket, occurred at regular intervals.


Bart and Bert have noticed an important fact for the prank: when we have sharp and weak noises, like crickets and drops of water, the human ear has difficulty determining the direction from which they come. This was very important to avoid locating the devices.


Back at Bart's house, let's see what happened to the "unwelcomed visitor".


Already in the room, when Skeeter laid down and turned off the lights, the dripper came into action.


- I must have left the faucet in the bathroom opened! - The boy said, getting up and going to the bathroom, but found nothing unusual.


He came back then and turned off the lights. The hassle was back. The boy waited a little to see if he could determine where the dripping came from and said very surprised:


- It isn’t raining! I believe!


He turned on the lights and tried to check where the sound came from: to his surprise, it stopped!


- Someone must have turned off the tap!


He laid down again and turned off the lights. Again, there was the annoying noise. Skeeter did not believe it. He quickly turned on the lights and sat up; The dripping had disappeared again.


- The thing is to forget this "damn" noise and sleep! - but he couldn’t! The initial effect of disappearing when he switched on the lights made him uncomfortable, and it drove him crazy.


After turning off the lights again and trying to sleep, which he failed, he turned on the lights and began to search for it! Of course, what he was looking for was some sort of "leak," and even if he found the little box over the wardrobe, he would probably not associate it with the noise.


- Damn it!


He spent the whole night turning the lights on and off without getting any sleep at all!


Next morning, Bart and Bert noticed the boy's red eyes and, one poking the other under the coffee table, risked to make a question:


- What's the matter cousin? Didn’t you sleep well?


- More or less! It must have been the excitement of the trip! - The boy did not want to say that there was something abnormal in the room.


“He did not confess, eh? Let’s wait and see” - Bart thought.


The day was not so full of tricks and pranks, for Bart and Bert’s luck, because Skeeter seemed a bit weary, as he had not slept all night long!


- It's time to change the devices! - Bart said calling Bert to a corner at the time when the visitor was distracted talking someone else.


Going to the boy's room, the two exchanged the dripper for the cricket, being careful to test it first. It worked well!


The fact that he had not slept all night meant that Skeeter was already very sleepy at 8 o'clock in that evening.


Apologizing, for leaving so early, he went to his room.


As soon as the boy turned off the lights, the noise began:


Cri! Cri! Cri! ...


Now this? It's not possible!


Skeeter turned on the lights and stood up! The noise stopped immediately. He still waited a little, he looked everywhere and nothing happened, he turned the lights off and laid down!


Cri! Cri! Cri! ...


Nervous, in a jump, he turned on the lights and again the sound stopped!


- Damn!


The boy then began, nervously, looking for the "bug" everywhere, and after a long time nothing was found.


- I'm going to have to sleep with this noise!


Rolling up on the blankets and putting the pillow over his head, he turned off the lights. The noise started again and it was "too boring" to be stuffy with a simple pillow.


The boy, however, gave up finding the source of "disturbance" of his sleep and tried to sleep anyway, only got some sleep much later, after being totally exhausted! After all, he had not slept at all the night before!


It was when he got up "broken" the next day that it occurred to him that such a noise could have been perfectly provoked by his cousin Bart and his friend Bert! After all, he noticed that they were a little weird the day before, even "accepting in a good way" his jokes!


- Fuckers!


He got up angrily, his eyes still red from the night asleep, and went downstairs for coffee.


- Did you sleep well? - Bert asked, already knowing what had happened, but the answer was not quite what he expected:


- Very well! - Skeeter said, staring at both of them, who realized that the boy was suspicious of something.


Bart and Bert looked at each other, knowing that if the "joke" was discovered, they could be in great trouble with Mrs. Johnson, Bart's mother, who was hosting the boy!


Skeeter, after the coffee, noticed that Bart and Bert tried to get rid of him, and soon he got in their way:


- Come here, we have something very serious to talk about!

The three of them then went to a quiet place and it was Skeeter who started:


- Very well, dear “cousins”! What a "flip" to make noise in my room at night!


- Noise? What noise? - Bert tried to disguise, but there was no way.


- Now! First the dripper, and it was not raining! Then the fucking cricket! Where did you hide the "bug"? It must be "tamed", because it stopped singing whenever I turned on the lights! ...


Bart and Bert were quiet.


Skeeter then, not wanting to go through another night of torture, yielded:


- It's ok! Let's make a deal! I do not do my pranks any longer, as long as you stop it!


Bart and Bert were irreducible:


- Please? - Skeeter insisted.


- It's ok! Let's make a deal, but you can’t tell anyone!


The three of them went to the guest room where Bart and Bert took out the cricket and also showed the dripper!


- This is good! Electronic tricks! You have to lend me that! - the boy had forgotten the annoyances completely, but Bart did not buy it:


- No! You won’t prank anyone for a long time! And there's more!


- More? But, what? - Skeeter was scared:


- You saw only two of our tricks! If you insist on making more of your pranks, we put our other "devices" into action!


The guest was startled and backing off he exclaimed:


- No, not that! I promise I'll be quiet!


Apparently everything was in peace, but in the countryside cities, where there are many "wild" animals, sometimes even very close to the houses, since "nature" is not far from around the corner.


The cricket noise that annoys humans may be too attractive to other species of the animal kingdom and this really had happened! ...


Soon, exhausted by a sleepless night and another ill-asleep, Skeeter went to bed, this time excited because he knew that he was in peace with his cousin and Bert assured him that, this time at least, he would not be bothered!


- Good evening! He said excitedly.


- Good evening! - The others answered, who were also happy to be free from the guest's pranks.


Not more than a minute had passed when a desperate cry was heard, and it came from Skeeter's room:


- Aah! Get that "thing" out of here!


Everyone ran, and when they opened the door of the guest room, they had an interesting scene before their eyes: Skeeter wearing pajamas trying to protect himself behind a chair while in the bed, looking at them with fear, a huge frog stood still. The frog had been attracted to the “singing" of the electronic cricket, thinking that there would be a "beautiful" dinner!


Bart looked at Bert, understanding what had happened, and commented:


- Again Professor Ventura's projects proved to be "too perfect" for the applications they are meant to be!


Despite receiving the huge "scolding" from Bart's mother, the two took the frog out of the boy's bed, trying to explain that they were not responsible for it!


When Skeeter left, the peace was restored, or at least it seemed: during the farewell the guest winked at Bert and threatened:


- Next time I'm coming reinforced!


Bart replied with another wink and said,


- We’ll be waiting to it! We have a good collection of snakes, lizards, spiders and other "bugs" to put on our “friends" bed!


Skeeter twisted his nose in fear and disgust, and said nothing else! Already on the bus that would take him back to the capital, he would take two plastic boxes out of his suitcase and examine them:


- I'm going to have some fun with it at home!


There were the "dripper" and "cricket" that Bart and Bert had "lent" to the boy!



Note: Articles on the site which teach how to build the cricket, for those who wish: ART296E (detailed), CB795E, CB762E and CB561E.




Circuit Bench