Help needed modifying circuit (For A Good Cause!!)

Thread Starter

Emir Ganovic

Joined May 22, 2019
5
Hello everyone,
This is my first post here, so here is the deal. I work as a volontary firefighter and we are trying to create a double flashing strobe light for one of our trucks/ vans. We found a circuit online, tried it out in Proteus, and to no surprise, it works. However, being that my knowledge on electronics is very basic, I need help converting the circuit from running off of a 6V battery to a 12V (Standard car battery), and to output 12V to blue LED strips instead of the pairs of red and blue LEDs (The current output is arround 5.07V DC according to Proteus). Any help would mean a lot.
 

ronv

Joined Nov 12, 2008
3,770
Hello everyone,
This is my first post here, so here is the deal. I work as a volontary firefighter and we are trying to create a double flashing strobe light for one of our trucks/ vans. We found a circuit online, tried it out in Proteus, and to no surprise, it works. However, being that my knowledge on electronics is very basic, I need help converting the circuit from running off of a 6V battery to a 12V (Standard car battery), and to output 12V to blue LED strips instead of the pairs of red and blue LEDs (The current output is arround 5.07V DC according to Proteus). Any help would mean a lot.
This may be a lot easier than you think, but we need a little more info.
How much current will your strips need? There appears to be no current limit for the ones shown in your schematic.
If we can establish that, and it is not too high probably the only thing you need is something to protect the circuit from high voltage.
Edit:
Maybe a data sheet for the LED strips.
 

be80be

Joined Jul 5, 2008
2,057
Both IC are able to work at 12 volts you need to add maybe a zenner to hold the 12 volts to 12 volts on the 555 and the 4017
But like above need to see what led strips your going to use.
Maybe use the 2n222 to trigger the gate of mosfet if the led strips are made for automobile.
 

ElectricSpidey

Joined Dec 2, 2017
1,904
Kind of a strange design…

R1 is not needed.
All of the 220R resistors should be replaced with diodes to avoid wasting current across outputs.
Place a single resistor at the base of the 222s.
Place resistor on each LED.
Carry out needs to be left open.

You will need to replace the 222s with something that has more ummmph, to drive your LEDs if they draw more than about 500mA.

Otherwise the circuit should work just fine at automotive voltage. If you are worried about overvoltage just use a regulator to power the signal portion of the circuit, and leave the LEDs on the vehicle voltage.
 
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Alec_t

Joined Sep 17, 2013
12,263
The capacitor would need to be replaced by one with a higher voltage rating (e.g. 25V) if the present rating is < 15V.
 

AlbertHall

Joined Jun 4, 2014
11,534
Automotiv 12V can be very noisy with large voltage spikes. I would want to add a good RC filter on the 12V input to the ICs - the LEDs could probably be run direct from the supply so a higher resistor value could be used to get better filtering.
 

Thread Starter

Emir Ganovic

Joined May 22, 2019
5
This may be a lot easier than you think, but we need a little more info.
How much current will your strips need? There appears to be no current limit for the ones shown in your schematic.
If we can establish that, and it is not too high probably the only thing you need is something to protect the circuit from high voltage.
Edit:
Maybe a data sheet for the LED strips.
Each strip is around 30 centimeters long, and is a 3.6W 6000K 60 diode per meter strip.
Any help and a new schematic would be great!
 

Dodgydave

Joined Jun 22, 2012
10,063
The chips will take 12V easy,,

Here is a drawing for the leds i would put a Series resistor in each led, try a 220 ohms to start with, and alter for brightness to suit lower resistance brighter leds, vice versa,,
, and use a TIP121 transistor or better still an IRL540 fet..

Same output driverDSC_0051.JPG for Blue and Red leds..
 
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sagor

Joined Mar 10, 2019
491
If using an IRF540, be sure to put a resistor from Gate to ground. Usually 10K or a bit more is enough to hold it down.
That said, make sure you have 10V on the gate for full RdsON (low resistance). If using logic levels (5V), look for a MOSFET with "L" (logic level) in it, like IRL540
 

MisterBill2

Joined Jan 23, 2018
9,529
The 12 volt LED strips do not need external resistors if they are designed to run on 12 volts. Modifying the board to replace resistors with diodes is not really needed, and the base drive to the 2N222s does need to be limited.
 

AnalogKid

Joined Aug 1, 2013
9,407
use a TIP121 transistor or better still an IRL540 fet..
The TIP121 has base-emitter resistors built-in to assure rapid turn-off. A FET will require adding a gate pull-down resistor (suggest 10K).

The commercial light bars run on 12 V directly, and have current limiting built in.

ak
 

AnalogKid

Joined Aug 1, 2013
9,407
First pass at a schematic. More simple 555 oscillator. I like bipolar transistors much moe than FETs in automotive environments, especially in a home-built circuit. Plus, you get free pull-down resistors. I need to add base resistors. More Later, including eliminating all of the diodes.

ak

upload_2019-5-23_19-18-23.png
 
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Thread Starter

Emir Ganovic

Joined May 22, 2019
5
Will be sure to follow up on the LED spec sheets, as my electronics knowledge is truly limited. One thing that bugs me is even though I do put 12 volts into a proteus simulation, the voltmeter shows only 5.07 volts at the LED terminals. Any clues?
 

ElectricSpidey

Joined Dec 2, 2017
1,904
If you are referring to the original schematic, the reason is probably the voltage divider created by the resistor configuration at the outputs of the 4017.

Or the 222s are simply overloaded because there are no limiting resistors on the LEDs.

Hard to say, because I don’t use Proteus.
 
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AnalogKid

Joined Aug 1, 2013
9,407
Here is an alternate output stage. C1, C2, and C3 should be ceramic for long-term reliability, rated for 50 V. C2 and C3 are decoupling caps for U1 and U2 (U3 does not need one). The 555 circuit is an alternate astable version that needs only one resistor. Each section of the 2004 is a darlington transistor rated for 0.5 A, with base current liming and pull-down resistors built-in. Only one section is on at a time. The overall circuit should have power transient protection added.

Update: The capacitors should not be electrolytic, but can be stacked metal film (I like Panasonic parts for this). Also, C2 is shown with the datasheet recommended value, but in fact, it can be almost anything. It can be another 1.0 uF part so you don't need to buy two different cap values.

If you want more output current capability, change U3 to a Sanken SMA4036 darlington array, rated for 2 A per output.

ak

Light-Bar-Flash-2-c.gif

Edit: Corrected reference designator.
 
Last edited:

Thread Starter

Emir Ganovic

Joined May 22, 2019
5
Here is an alternate output stage. C1, C2, and C3 should be ceramic for long-term reliability, rated for 50 V. C2 and C3 are decoupling caps for U1 and U2 (U3 does not need one). The 555 circuit is an alternate astable version that needs only one resistor. Each section of the 2004 is a darlington transistor rated for 0.5 A, with base current liming and pull-down resistors built-in. Only one section is on at a time. The overall circuit should have power transient protection added.

ak

View attachment 178091
As stupid and boring as my questions may sound, each capacitor used here is basically a ceramic 50V rated one? And since im bad with schematics, everything with a ground terminal is connected to the negative battery terminal?
 

AnalogKid

Joined Aug 1, 2013
9,407
Yes and yes. +12 V is wherever your vehicle power is coming from, and the GND symbol is the return. Not shown are the Vdd and GND connections to U2. This is because many schematic drafting programs connect them invisibly to eliminate a bunch of clutter on the page. All of the unconnected pins are either unused outputs or treated internally so it is ok to let them float.

Where are you located?

ak
 
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