Traffic lights

[madmikejt12]

hi, we are using the chip factory to make traffic lights and other models for years 7, 8 and 9 to program so they can get used to the chip factory, but there is a problem, when we swap the LED's for bulbs, there is not enough current to power them, we sorted this by using 3 transistors to amplify the current (see diagram), but when the red and amber are on at the same time,they are dimmer than what they should be, is there a way to resolve this problem without using 3 seperate batteries?

This is the board we are using: **broken link removed**

Circuit we used:
**broken link removed**

 

[Nigel Goodwin]

For a start, make sure you have a resistor in the base lead of each transistor.

For the bulb problem, it sounds like your battery is too small to provide enough current?, I'm presuming you're only using a tiny PP3 type?.

 

[madmikejt12]

sorry, forgot to add the resistors for all the transistors, when i was making it, i did use 3 resistors (1 for each transistor) and yes, i am using a pp3 battery, would a 9v DC power supply work (from the mains) or would i still have the same problem?

i thaught it was because there was 9v going into each bulb, and when 2 came on, the voltage was splitting into 4.5v for each bulb?

 

[Nigel Goodwin]

sorry, forgot to add the resistors for all the transistors, when i was making it, i did use 3 resistors (1 for each transistor) and yes, i am using a pp3 battery, would a 9v DC power supply work (from the mains) or would i still have the same problem?

A PP3 will only provide fairly small amounts of current, a suitable rated regulated mains PSU will solve the problem - an unregulated one may well be as bad as a small battery!. It will also be MUCH, MUCH cheaper, a PP3 battery won't keep bulbs running for very long (only a fairly low number of minutes!)

i thaught it was because there was 9v going into each bulb, and when 2 came on, the voltage was splitting into 4.5v for each bulb?

No, it's due to the voltage drop across the batteries internal resistance.

I hope you're one of the kids, and not the teacher? 8)

 

[madmikejt12]

yes i am one of the kids, :lol: lol... although the teacher didnt seem too sure what to do :shock: !! unless he had his mind somewhere else :lol:

 

[madmikejt12]

thanks for your help looks like i'll be finished next week i was the only one trying that circuit, the teacher told me to have a go to see if it worked so all i've got to do is solder it how it is to stripboard and swap the pp3 connector for a suitable power socket

 

[Nigel Goodwin]

yes i am one of the kids, :lol: lol... although the teacher didnt seem too sure what to do :shock: !! unless he had his mind somewhere else :lol:

Well, to be honest, the quality of electronics teaching in most UK schools is incredibly poor - most might have done a one day course on it!.

 

[madmikejt12]

lol, our teacher came to our school 11 years ago to teach electronics, did it once then it stopped so he's been teaching woodwork and graphics and it was only this year they decided to do it again, he said its changed since last time he taught it.

Thanks again for your help

 

[suicidalmonkey]

...when the red and amber are on at the same time...

Although you have already sorted out this problem, I just thought i'd put in my two cents.

Is this really a problem anyway? In Australia (not sure if it's the same anywhere else) their is only one light (red, amber or green) on at a time anyway.

 

[madmikejt12]

i dont know about all the traffic lights, but some (or all) in the uk go red, red & amber, green, amber, red.... this is so you know wheather to get ready to stop or get ready to go when approaching the lights

 

[MikeHibbett]

The UK sequence is different from many countries. In Ireland they follow a similar to the previous posters (suicidalmonkey).

I heard somewhere that it was so that you could tell which direction the lights were going; If only Amber was alight, are they turning off, or on?

In Ireland (well, Dublin any way) the meaning of traffic light colours differs to the uk too )

 

[eblc1388]

Since we are on the subject of UK changing traffic light color, you can also use the PIC to mimic correctly the flashing of amber light soon after red light has gone ON.

I don't know whether flashing amber light is an unique feature in the UK system only.

 

[MikeHibbett]

>I don't know whether flashing amber light is an unique feature in the UK system only.

They have it in Ireland too. It is supposed to mean 'proceed but give way' but seems to mean 'now is a good time for an accident' in my experience, unfortunately!

 

[madmikejt12]

the flashing amber is only for pedestrian crossings, we are just doing 1 traffic light (each) the main reasons are to get us used to using the chif factory to program chips and when weve done it, the school can use them for lower years to program traffic lights instead of usind the LED's on the demo board

 

[audioguru]

Why are you using high-current lightbulbs anyway? Is it because the low-current LEDs burned-out because you forgot to use current-limiting resistors in series with them?

 

[JimB]

>I don't know whether flashing amber light is an unique feature in the UK system only.

They have it in Ireland too. It is supposed to mean 'proceed but give way' but seems to mean 'now is a good time for an accident' in my experience, unfortunately!

The craziest traffic lights I have seen are in Egypt.
I am told that officialy the light are "advisory", and every one just ignores them!

JimB

 

[madmikejt12]

no i added the resistors, its just we're making fairly big lights with coloured plastic behind a piece of wood in the shape of a traffic light with circles cut out of it (and of course a base, sides and a lid) so we needed a bigger light source

 

[madmikejt12]

>I don't know whether flashing amber light is an unique feature in the UK system only.

They have it in Ireland too. It is supposed to mean 'proceed but give way' but seems to mean 'now is a good time for an accident' in my experience, unfortunately!

The craziest traffic lights I have seen are in Egypt.
I am told that officialy the light are "advisory", and every one just ignores them!

JimB

lol, sometimes it seems like that here!!!!

 

[audioguru]

we needed a bigger light source

I don't think big lights and a dinky little battery match very well. Did you try a real power supply to solve your dimming problem?