'Electric fence' warning buzzer and lights

Didn't dawn on me he is using 9volt battery
and the darkness rolls in
good catch Boncuk

Boncuk said:

Here is a revised schematic. Connect three strings of LEDs in parallel, two of them containing 3 LEDs and one containing 2 LEDs.

Click to expand...

Hmmm, an engineering change order at the 11th hour. Suddenly I look pretty smart for keeping all the resistors I bought in 1984

Thanks again Boncuk. I should be able to implement this variation easily.

MrDEB said:

Didn't dawn on me he is using 9volt battery
and the darkness rolls in
good catch Boncuk

Click to expand...

Four eyes usually see more than two.

if one pair sees 20/20 does that mean two pair see 10/10 or 40/40??

MrDEB said:

if one pair sees 20/20 does that mean two pair see 10/10 or 40/40??

Click to expand...

Nope,

you mustn't double the divisor. If one pair sees 20/20 two pairs see 40/20.

Nobody can beat a recce pilots's vision.

WHAT is a recce?

reconaissance

thats what the airline pilots were doing on their laptops after flying 150 miles past mininapolisis last month


lol

MrDEB said:

thats what the airline pilots were doing on their laptops after flying 150 miles past mininapolisis last month


lol

Click to expand...

Nope, they were playing Mahjongg! Isn't it Minneapolis?

Reminds me to the radar navigator/bombardier:

He talked the pilots into the target: "Right on course to the target - now a touch left; roll out now - 1 mile to go to the target - just a small touch right; roll it out - 1/4 mile to the target - ... zs - zs - zs - and now a little back".

I completed the wiring and assembly at about 2:30 am on Thanksgiving morning, and the completed toy (2x2' Dinosaur paddock with LEDs and buzzer) was given to my 5-year-old nephew as a surprise present about midday.

He immediately knew it was for his toy dinosaurs, though he couldn't believe at first that it really was his and that he could keep it. The look on his face was great - I think the only time he stopped grinning the whole day was when he was concentrating on fierce battles (we had also given him a bucket of army men figures because, after all, dinosaurs must have something to eat). He was so happy we thought his head might burst.

He loved the light and buzzer, and the circuit Boncuk designed got a really serious workout!

So thanks again everyone, for the help making a little boy very, very happy!


Now, I have two technical questions that occurred to me as I was putting the circuit together:

1) There are three capacitors (C3, C4 and C5) that are essentially in parallel between VDD and GND. As I understand it, their combined capacitance is 49.947nF. What is the purpose of having three caps?

2) Between T1 and VDD there is a diode D20. There is not a similar diode between T2 and VDD. I know what a diode does, and I assume here it must have something to do with the buzzer that is also connected to T1, but I don't understand what/why.

Thanks again!

Hi ESchreiber,

C5 is a general purpose electrolytic capacitor keeping the supply voltage as stable as possible even with a long cable from the power source.

C3 is a decoupling capacitor for the timer IC (NE555) and C4 serves the same purpose at the counter IC (HCF4017). C3 and C4 should be placed as close as possible to the IC's power pins.

C5 is less critical in that particular circuit because only little current has to be supplied by the timer IC. With a higher load C5 should also be placed as close as possible to the timer ICs power pins.

D20 is a prophylactic safety measure to eliminate possible back EMF being produced by the buzzer circuit and probably destroy T1.

You might omit it, but if it was required for the given reason transistor T1 might have died in the meanwhile. until you notice it was really required.

Boncuk

Boncuk said:

C3 is a decoupling capacitor for the timer IC (NE555) and C4 serves the same purpose at the counter IC (HCF4017). C3 and C4 should be placed as close as possible to the IC's power pins.

Click to expand...

Ah, 'decoupling capacitor' is a new concept for me. I placed C4 pretty well in my breadboard layout. C3, not so much

Boncuk said:

D20 is a prophylactic safety measure to eliminate possible back EMF being produced by the buzzer circuit and probably destroy T1.

Click to expand...

I figured it must be something like that, but didn't know the specifics.

Thanks for taking the time to help me learn some new stuff!