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Circuit Owner
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Discussion Starter · #1 ·
I notice in the chipped cars thread that some people simply fit a diode to analogue cars with lights so the lights are protected from reverse current.

I understand how diodes work and that you need a separate diode because the reverse current in an LED will blow it.

BUT - by doing it this way isn't the light only getting half of the sine wave from the A/C? Presumably this will cause the lights to flicker (albeit it higher frequency than a TV screen). I also assume this will only allow the light to draw half the power so aren't the lights dimmer as a result?

I have recently installed lights and a chip in a car and used a bridge rectifier to make sure the LEDs receive constant power. Is this a better approach or am I wasting effort?

The added bonus of using the bridge rectifier by the way - is that it allows the lights to run on an analogue track regardless of which direction you place it - no faffing around with changing polarity needed if you want to run the track in reverse.
 

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I have a variety of lighting hook up on my chipped cars,
But the easiest option is as youve done use the bridge diodes as a 12V supply then adjust your resistors to get the desired current.
Somtimes I use the 5V regulator as a supply but when doing this LEDs must be wired in parallel espcially with white ones as the forward voltage is 3V so series woudnt work. Also if I have an ICP chip then I use the HL and BK outputs and just make sure the total current for each pair of LEDs is not greater than 25mA, 10mA in a white LED from farnell seems to work just right. so thats a total of 20mA so thats OK
 

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Greg Gaub
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And I'm a luddite risk-taker, who doesn't add diddly. If the lights don't work when I put the car on the track in the direction I run them, I swap the pickup leads. Haven't blown a light yet.
 

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What type of diodes do you use for the bridge rectifier?

I have another application where I want to take 12v from the track to use as 12vdc on a circuit rather than power separately on a 12vdc power supply. I figured I could use a bridge to do this but did not know which diodes to choose. Presumably the diodes you select depend on the current load on the other side, right?

Any direction you can provide will be appreciated. Thanks.
Cheers!
 

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Circuit Owner
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Discussion Starter · #5 ·
Hi Sealevel,

The diodes I chose were Zener diodes rated at 12v 1.3w although I believe these voltage ratings are misleading because these diodes can handle anything up to 30v.

I guess to some extent it depends on how much current is being drawn. As the LEDs I am using will not draw anywhere near 1.3w - even when I use 6 of them, I just went for cheapest and smallest!
 

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Thanks Mr. Modifier.
I have an idea I have posted on the Powered Flipper thread (link) which uses both a diode rectifier and some diodes to prevent reverse current so these might just do the trick.

Now to read up on rectifier bridges so I do it the correct way!

Cheers and thanks again!
 

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The in car chip has a diode bridge built in so no need to add another. I woulnt use zener diodes for a bridge, just use rectifier diodes with a rating of 1A or more. Zener diodes are designd to be used a voltage clamp and are rarely used in forward bias mode. If i have a little time at lunch i will try to add an anotated drawing of where to add lights on a chip
 

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Living the Life!
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Circuit Owner
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Discussion Starter · #9 ·
Thanks Greg - and yes - I would make these connections except I have a pile of the single seater in-car chips which don't have the pads for lights. Plus - the Endurance Start cars have two structural chassis rails which are the perfect size for the single seater chip to sit between - the saloon chip would require cutting the chassis and weakening it.

When I find a car I want to chip that has space for the saloon chip I will connect to the pads.

mpg200 - same thing - I know the chip has a rectifier built in but, as I am using the single seater chip, I am connecting the lights across a bridge rectifier that is in parallel with the chip across the braids.

Back to my original question - given the fact I need to connect my lights across the braids - is my bridge rectifier a better option than straight diodes which might only feed the lights with what I imagine is half of the available electrical sine wave?
 

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If you use A single diode then yes you will only get half the ac wave converted to usable LED power, This however may be enough. Are you using the lights 'as is' i.e. on the little pcb with 2 tiny SMD resistors and 2 really thin wires? if so then adding a bridge is the easiest way to get full power lights. If you're a bit of a tiger, then flip over the single seat chip and attach the LED board wires to +12V(pin 8 on 8 pin device) and 0V (pin 2 on 8 pin device) 8 pin device is the 5V regulator it takes 12V in (pin 8) and gives 5V out (pin 1) attaching the wires here gives you a nice stable 12V DC supply for free, no bridge needed. Pin 1 on 8 pin device is marked with a dimple on the case then numbered anticlock wise round the case.
 

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..... that 8 pin device is the heart and soul of your chip, the programmable PIC16F630
 

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Discussion Starter · #12 ·
QUOTE (mpg200 @ 26 Apr 2012, 13:49) <{POST_SNAPBACK}>If you use A single diode then yes you will only get half the ac wave converted to usable LED power, This however may be enough. Are you using the lights 'as is' i.e. on the little pcb with 2 tiny SMD resistors and 2 really thin wires? if so then adding a bridge is the easiest way to get full power lights. If you're a bit of a tiger, then flip over the single seat chip and attach the LED board wires to +12V(pin 8 on 8 pin device) and 0V (pin 2 on 8 pin device) 8 pin device is the 5V regulator it takes 12V in (pin 8) and gives 5V out (pin 1) attaching the wires here gives you a nice stable 12V DC supply for free, no bridge needed. Pin 1 on 8 pin device is marked with a dimple on the case then numbered anticlock wise round the case.

I'm using the LED "as is" but it's not the tiny little SMT ones - it's a 5mm superbright x 2 on the front (hey I want it to look like a headlamp and I am mounting it in a body with no lens - just a sticker). The superbrights are awesome and light up the track for about a metre but they probably pull a ton more current than the weedy SMT's (if my pathetic scaley viper lights are anything to go by).

The rears are either rectangular 5mm LEDs or 3mm round ones. Again because the Start cars have no light lenses - just plain bodywork that I need to make holes in.

Intriguing that I could tap off the single seater chip - but would the current drain of 2 x 6000mcd and 4 x 2000mcd LEDs be too much and fry my expensive chip?
 

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Living the Life&#33;
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All the Scalextric chips can be tapped in this way. They all have the same PIC16F630 chip therefore the same I/Os, except the F1 DPR but if you get MIH's circuit diagram for the Saloon chip, you can soon trace what's what on the PIC.

View attachment 9992 View attachment 9993
 

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Circuit Owner
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OK you've got me really interested now.

Assuming I can find a tame pixie to do the soldering for me (kidding - I have a blown chip I can practise on first).

Can I assume the 12v DC into the 8 legged thingy is there at all times the braids are in contact with the rails?

Can I power all those LEDs off the PIC chip without causing meltdown?

Damn - add another 2 LEDs - for brakes!

2 x 6000mcd for headlights. 2 x 2000mcb for running lights. 1 x 600mcd for ID light (one of 6 APB colours to help identify the car in the dark) and 1 x 1000mcd for flashing rear light a la F1 wet running lights.

Add 2 more 2000 mcd red for brakes and I have the full monty.

If the chip won't stand the heat I could always run all the lights off the bridge rectifier and just tap into the chip for the brakes.

On the subject of brakes - do they work when you are off the throttle or only when you press the brake button? I only wondered because I was thinking of setting up SSDC to use the brake button for track calls seeing as hardly anybody uses the brake button.

Oh - one more thing - what voltage does the brake out pin deliver? I will need to recalc the resistors as mine are done for 12v. I assume I can ground the brakes anywhere on a convenient return (is that why you highlight the resistor with 5v - if so which side do I ground to?)

Sorry Greg - more questions. Would love to try it out over the weekend - I have 3 more to light by next Wednesday (and possibly 3 more to add brake lights to as well)
 

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Ting Tong
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hi
if you use the chips in mih spec to power lights then you will not need to add extra lights for the brakes to work.

One set of led's do both tail and brake..
 

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QUOTE (mpg200 @ 26 Apr 2012, 00:53) <{POST_SNAPBACK}>The in car chip has a diode bridge built in so no need to add another. I woulnt use zener diodes for a bridge, just use rectifier diodes with a rating of 1A or more. Zener diodes are designd to be used a voltage clamp and are rarely used in forward bias mode. If i have a little time at lunch i will try to add an anotated drawing of where to add lights on a chip
So the rectifier diodes should be for 12v or will any voltage work?
I have seen lots of rectifier diodes on "that auction site" which are for 100v, 400v, etc. and current ratings of 3A etc.
In other words, when working with diodes do the voltage and current ratings have to correspond to that of the car or track or is a higher rating better?

Many thanks!
Cheers!
 

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Mr Mod .... were to start?

i) I would doubt that 12v would be used anywhere near ICs; they are usually rated to 5v or 3v.
ii) There is about 200mA of current to play with, at best.
iii) Ordinary brakes extinguish on zero throttle.
iv) The Saloon chip outputs 5v on the head lights and 5v on the brakes; I see no reason to expect more than that.

Would you like to send me that duff chip you have and I'll see if it can be mended and/or uprated? I can send you a knobbed chip for your Pixie to practice on
 

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QUOTE (sealevel @ 26 Apr 2012, 17:56) <{POST_SNAPBACK}>So the rectifier diodes should be for 12v or will any voltage work?
I have seen lots of rectifier diodes on "that auction site" which are for 100v, 400v, etc. and current ratings of 3A etc.
In other words, when working with diodes do the voltage and current ratings have to correspond to that of the car or track or is a higher rating better?
Normal rectifier diodes ratings (100V etc) are the rated maximum reverse voltage. i.e. the maximum voltage they can block (reverse biased) before junction breakdown. In a rectifier diode when the junction breaks down the diode is broken and useless. A zener diode is very different beast, they are designed to breakdown at a rated voltge (12V 5.1V etc). when a zener junction breaks down is is not useless it behaves as a clamp, and limits the voltage to the beakdown voltage. So just use normal rectifer diodes they are cheaper and can carry more current in normal use (forward biased)
The highest voltage your car can see is about 30V -15V to +15V so as long as your diodes are rated higher than that you'll be fine
The diodes on the chips are 50V rated maximum blocking voltage.

Oh the 8 pin device on the chip is a 7805 voltage regulator in SOIC8 package
The larger device with 14 pins is the 16F630 PIC
A 12V tap of the input to the 7805 (Pin 8)
voltage regulator data sheet
Will have loads of power available for all your LED needs
the only parts between that pin and the track are the bridge diodes and the wires to the braids.
 

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Thanks mpg200 ...... d'oh, D'OH! .......... I must look at the diagrams before I type
The 8 legged beastie is an LM78L05

Pin 1 is +5v out, Pin 8 is ~+12v in and Pin 2 is ground. In MIH's instructions for flashing an F1 chip, he suggests using Pin 2 for 0v.

View attachment 9996
Here is the ciruit diagram.
 
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