How do you choose the correct components?

Thread Starter

TwoTon

Joined Aug 6, 2015
119
I plugged everything into the online simulator to see what kind of power usage I should expect - for how long the 9v battery will last. Not sure what to make of the simulator and how it figures things. When I put the 10uF capacitor in the circuit the amperage goes from 406 uA to 36A. Yes, that is a full 36 amps. I cannot see how that is the case, but it sure made me scratch my head.

Obviously it is not calculating right because I should be using more than half a mA in lighting up those 3 seven segment LED's.

Interesting none the less.
 

Thread Starter

TwoTon

Joined Aug 6, 2015
119
The displays would be 7 segments * 20 mA/segment * 3 displays = 420 mA

A 9V battery won't make the grade. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwid0LmF-pjMAhWFcz4KHS17BYAQFggjMAE&url=http://data.energizer.com/PDFs/EN22.pdf&usg=AFQjCNHlBWIAXEm0kLkrAKV5ahKJW5Ctzg&sig2=ikwkn4IfkIXnElTiEsAP-Q

Probably a bad calculation. Because you have 0, 1, 2 and 3. 0 has 6 segments on.
Yea, thats what I am starting to think. Oh well, I can power it fine with a wall wort. Once its all up and done I'll test the current just to see what it might be like.
 

Thread Starter

TwoTon

Joined Aug 6, 2015
119
Had another thought come to mind. I'll be using a wall transformer/supply, found a 9vdc and even have the female adaptor I had saved from other projects. My question is how critical is it to maintain 9v? I have not measured the output of the supply yet, but I know that generally they are higher than listed. I have worked with voltage regulators before, and I believe I have some around, is this something that is needed in this particular circuit?
 

MrChips

Joined Oct 2, 2009
20,263
As you say, walwarts output will be higher that stated.
Plug it in the wall and measure the voltage.
I would look at a 6-8V adapter to start with.
My circuit will tolerate up to 18V but the LEDs will be progressively brighter.
 

Thread Starter

TwoTon

Joined Aug 6, 2015
119
Its alive! I'll get some pictures of it once I set it up on the track. I finished the wiring and all this morning and hooked the photo sensors up on the bread board to test the circuit and LED's. I wonder how much the differences in resistor and sensor values will effect the speed of the circuit in a close race. I am not sure how you would tune such a thing, but hopefully its so minuscule it wont matter.

Thanks again Mr Chips. Kids are gonna love it and I had fun building it.
 

Thread Starter

TwoTon

Joined Aug 6, 2015
119
I really messed up on my board layout. I was really crowded, but made it work. Im still not sure if I like the reset switch configuration, but it works for now. I think I'll get a long two conductor and run the reset back to where the cars begin.
 

Thread Starter

TwoTon

Joined Aug 6, 2015
119
Derby Day went on without a hicup from the finish line indicator! Very happy. There were actually quite a few races where everyone said they were sure glad they did not have to judge the winner.

Many thanks again. Very easy circuit to build and well worth it. I have already started planning another circuit to show actual times. It won't be for anything other than to see the differences between cars and different races in different groups.

I do need to redo my LED's, to make them bigger and add a bezel. But the setup worked well enough as is.
 

hp1729

Joined Nov 23, 2015
2,304
Hello guys. I think I have gotten close to my goal but would like some help with it. I used a online circuit simulator program to develop it. I am not sure how accurate it is, or if it would tell me if something is impossible(it does seem to indicate obvious errors). Here is a picture of it.

View attachment 104242

In the online simulator, it seemed to work. I could not tell if there was an issue, the simulator seemed to be bogged down with each lane I added.

I am trying to put together a simple circuit for a three lane pinewood derby track finish line. I have found multiple types of circuits that come close to what I am wanting, but nothing exactly. If you guys could tell me that this looks doable, and help me pick out the components that would make it work, I would be very grateful and so would around 60 or so kids that will be racing their cars.

The idea is there is a main power/reset switch, that will be pushed after each race. I can see where this might need to be located in a different position, or even have one for each separate circuit.

The other three switches will be photo transistors(I just used push button switches in the simulator). Triggered by the car passing over the top and blocking out ambient light.

Then each lane will have two LED's. One is for first place, the other is for second place. The third place lane will have no LED lit.

The idea is that once a car triggers the first place LED, then it "locks" out the other lanes first place LED. Then the next car will trigger the second place LED, and lock out the others.

I needed a way to see first and second, and I only could find circuits that showed first place winners. I have seen cars come very close at the finish line and this will save a lot of arguing I hope.

Please, if you guys could, help me out. I am not sure how to spec out what transistors and mosfets I need. And of course, if there is an easier way, please by all means let me know. Thanks a bunch.
My first idea would be logic chips also but this looks like a good place for a microcontroller.
 

hp1729

Joined Nov 23, 2015
2,304
Hello guys. I think I have gotten close to my goal but would like some help with it. I used a online circuit simulator program to develop it. I am not sure how accurate it is, or if it would tell me if something is impossible(it does seem to indicate obvious errors). Here is a picture of it.

View attachment 104242

In the online simulator, it seemed to work. I could not tell if there was an issue, the simulator seemed to be bogged down with each lane I added.

I am trying to put together a simple circuit for a three lane pinewood derby track finish line. I have found multiple types of circuits that come close to what I am wanting, but nothing exactly. If you guys could tell me that this looks doable, and help me pick out the components that would make it work, I would be very grateful and so would around 60 or so kids that will be racing their cars.

The idea is there is a main power/reset switch, that will be pushed after each race. I can see where this might need to be located in a different position, or even have one for each separate circuit.

The other three switches will be photo transistors(I just used push button switches in the simulator). Triggered by the car passing over the top and blocking out ambient light.

Then each lane will have two LED's. One is for first place, the other is for second place. The third place lane will have no LED lit.

The idea is that once a car triggers the first place LED, then it "locks" out the other lanes first place LED. Then the next car will trigger the second place LED, and lock out the others.

I needed a way to see first and second, and I only could find circuits that showed first place winners. I have seen cars come very close at the finish line and this will save a lot of arguing I hope.

Please, if you guys could, help me out. I am not sure how to spec out what transistors and mosfets I need. And of course, if there is an easier way, please by all means let me know. Thanks a bunch.
To give you an idea of how few parts a microcontroller design would be, look at this. Page 1 is the controller. Page 2 is the circuitry that would go in each lane and would be the same no matter what controller design you went with.
 

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Thread Starter

TwoTon

Joined Aug 6, 2015
119
My first idea would be logic chips also but this looks like a good place for a microcontroller.
Yea, I have been looking around to see if some logic chips would work, but I cannot find any circuits for such a thing. Really, the start and stop function of the circuit is setup already. So all I need is a millisecond counter circuit to 'integrate' into the current one. I'd keep the 1st, 2nd, and 3rd place indication - just add the time in milliseconds over it.

I have been looking into microcontrollers. I have never messed with them, and it seems there is more to them than what meets the eye. I guess I'll dive in with an Arduino. They all look like they have different ways of programming them and stuff. But the Arduino has the biggest support base?

At least I have a while to work on it. This time I wont wait till the last few weeks.
 

hp1729

Joined Nov 23, 2015
2,304
Yea, I have been looking around to see if some logic chips would work, but I cannot find any circuits for such a thing. Really, the start and stop function of the circuit is setup already. So all I need is a millisecond counter circuit to 'integrate' into the current one. I'd keep the 1st, 2nd, and 3rd place indication - just add the time in milliseconds over it.

I have been looking into microcontrollers. I have never messed with them, and it seems there is more to them than what meets the eye. I guess I'll dive in with an Arduino. They all look like they have different ways of programming them and stuff. But the Arduino has the biggest support base?

At least I have a while to work on it. This time I wont wait till the last few weeks.
Arduino is good.
 
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