Help me with LED Strobes

[delokaver]

Hi all,

can some one draw me the schematic for various led strobes ???
SOS pattern, Police Pattern, etc

if possible do not use any PIC, since very dificult to get this type of componen here.
can use LM555 and CD 4017 or some thing like that possibly.

thanks for the help

 

[Boncuk]

Hi delokaver,

please describe the SOS and police patterns. I have no imagination what they could be.

Police- & rescue cars in Thailand have no pattern, just a couple of randomly flashing strobes on top of the cars.

Boncuk

 

[delokaver]

hi boncuk,
sos that i means is : like 3 times flasing and stop for a while and then 3 time flasing again, some thing like that.

and yes as you means like flashing lamp in the roof of the police car

do you have this ???

 

[Boncuk]

No, I haven't, but I can make a circuit of this kind. Doesn't require an MCU.

SOS in morse code is: ...---..., meaning three short pulses, three long and three short ones again.

 

[delokaver]

great, could you please draw the schema for me ???

thanks

 

[Boncuk]

Hi delokaver,

here is something you can play with for a while.The circuit uses an astable MVV (NE555) with variable frequency from 9 to 25Hz connected to a decimal counter (CD4017).

Three output pins spaced two outputs (clock cycles) apart and connected to the LED via diodes (to prevent current flow into the output) make the LED flash three times, then pause and return to a new cycle.

Making a true SOS light signal requires at least three counters. Dashes have to be three times longer than dots according to morse rules. To obtain the required pulse lengths and pauses lots of output pins must be left unconnected.

I suggest to use an MCU for a light pattern like that.

Another easy to do circuit is double flashing with alternating LEDs, like it is used as 'camouflaged headlights' of police cars (at least I saw that on TV - very impressive)

The LED used for the circuit is a low current (2mA) LED at a forward voltage of 2.4V.

Connecting a normal LED (20mA) and using a 9V battery you might omit the current limiting resistor. That LED will illuminate a bit dim.

Boncuk

 

[Gayan Soyza]

Making a true SOS light signal requires at least three counters. Dashes have to be three times longer than dots according to morse rules.

Thats true.

Also to take the real effect of strobe feeling the LED's must pulse like this.

(LED OFF TIME) = 3 X (LED ON TIME).

Otherwise it will notice like just flashing LED's.

 

[Ubergeek63]

Making a true SOS light signal requires at least three counters. Dashes have to be three times longer than dots according to morse rules. To obtain the required pulse lengths and pauses lots of output pins must be left unconnected.

Not true.

If you modulate the high time of the oscillator with the 4017 outputs and gate the LEDs from the high time you can do it in a single counter.

 

[vne147]

I didn't spend a lot of time and effort thinking about this of making this schematic but something like this might work for the SOS pattern you mentioned. You can vary the duration of the short and long pulses by adjusting the potentiometers.

 

[vne147]

After thinking about it a little more. You could probably eliminate D1 through D6 altogether in the schematic and instead just connect those wires directly to each LED's cathode.

 

[Boncuk]

Not true.

If you modulate the high time of the oscillator with the 4017 outputs and gate the LEDs from the high time you can do it in a single counter.

I'm curious, please show it.

 

[Boncuk]

I didn't spend a lot of time and effort thinking about this of making this schematic but something like this might work for the SOS pattern you mentioned. You can vary the duration of the short and long pulses by adjusting the potentiometers.

Sorry vne147,

that circuit flashes nine LEDs in equal sequence. (LED chaser). The morse code again is: ... --- .... (from one transmitter to one receiver. Here you have 9 receivers.) The 4017 counting pattern looks different.

There is no break between 'signs'. If one output goes low, the next one goes high simultaneously. You could wire three outputs together using diodes to obtain a dash, omit one output and use the following to 'write' an 'e' (single dot).

So simulating a true SOS will take three CD4017, occupying a total of 28 outputs for an SOS and 5 time units break between transmissions.

Also the CD 4017 doesn't take care of pulse length, just freqency. It advances one count with each positive going pulse edge. So using 'PWM' is nulled by the 4017. Its outputs have a duty cycle of exactly 50%, no matter if you use duty cycle of 99% or 1%.

Here is the SOS as it would look on an oscilloscope. Normally the letters have to be spaced by 3 time units. (Words must have a spacing of 5 time units.) SOS is considered to be one letter and therefore spacing is equal.

To achieve just an 'S' requires 5 output pins: 0,2,4 for the active phase, and 1 and 3 for the pauses between pulses. The schematic I made in a former post represents exactly one 'S' followed by a long break.

Boncuk

 

[vne147]

Boncuk,

Like I said I didn't spend that much time thinking about it. It was just an idea. I don't think it would flash 9 LEDs in equal sequence. the middle three would have a longer delay between them. However after thinking about it a little more, I'm fairly certain you can accomplish the SOS pattern with only 2 4017's. I don't have time to make up a schematic right now but I'll post it in a day or so.

 

[Boncuk]

Boncuk,

the middle three would have a longer delay between them.

No! That can only happen if the clock cycle is changed.

 

[delokaver]

hi all,

thanks for your help and sugestion, realy appriciate that. but if i need to paralel the LEd used did i should use a transistor to handle that ?? 2n3904 some thing like that ???
i saw some schematic outhere related to this topic, the 2n3904 can be handle 4 bright LED with 2 led in series, and now another question, if i need to double the LED used should i double the 2n3904 also ?? with paralel circuit ?? or how ???

 

[delokaver]

hi vne147,

after take a look with your circuit, i found some thing strange, what does T1 means above the 555 ??? is this a transistor ro what ?? could you please help me and let me know ??

 

[vne147]

hi vne147,

after take a look with your circuit, i found some thing strange, what does T1 means above the 555 ??? is this a transistor ro what ?? could you please help me and let me know ??

Delokaver,

T1 is a triac. When T1 is active it essentially shorts across one of the pots next to the 555 and has the effect of increasing the frequency of the pulse train coming out of the 555. That is how you get the ... --- ... pattern that you are looking for. For the ... part the triac is active and allows current to pass. For the --- part the triac is not active, current has to pass through the extra pot, and the frequency of the pulse train being output by the 555 decreases.

Boncuk, what do you think about this circuit?

 

[Ubergeek63]

I didn't spend a lot of time and effort thinking about this of making this schematic but something like this might work for the SOS pattern you mentioned. You can vary the duration of the short and long pulses by adjusting the potentiometers.

A more standard 555 circuit and simply routing the diodes to a second timing resistor instead of an SCR (which probably won't work do to SCR limitations) and taking the output of the 555 to drive the LED as well will give him the "SOS" flashes.

 

[vne147]

A more standard 555 circuit and simply routing the diodes to a second timing resistor instead of an SCR (which probably won't work do to SCR limitations) and taking the output of the 555 to drive the LED as well will give him the "SOS" flashes.

Can you give an example of simply routing the diodes to a secondary timing resistor? I don't think I'm following you. Also, the symbol in the schematic is a triac, not an SCR. I don't think they are the same thing. I'm not sure what limitations you are referring to and if they apply to triacs as well. Could you please elaborate?

 

[Boncuk]

Delokaver,T1 is a triac.* When T1 is active it essentially shorts across one of the pots next to the 555 and has the effect of increasing the frequency of the pulse train coming out of the 555.* That is how you get the ... --- ... pattern that you are looking for.* For the ... part the triac is active and allows current to pass.* For the --- part the triac is not active, current has to pass through the extra pot, and the frequency of the pulse train being output by the 555 decreases.Boncuk, what do you think about this circuit?

Hi vne147,

I've never played with triacs and low voltage. May be the circuit will work that way.

The simplest way to make the SOS-pattern is 99% mechanic and 1% for a current limiting resistor and an LED.

Use a toy motor with a reduction gear and drive a circular PCB with the code etched. Use a slider to contact and drive the LED.

Using it correctly you can make a surprise for your wife. Etch this pattern: "did did - did dah did did - dah dah dah - did - dah did dah dah - dah dah dah - dah did dah dah". (did is a dot and dah is a dash)

This circuit is almost immune to power variations and spikes.

It was used on board of the GAF (German Air Force)-20-man life rafts in the emergency transmitter.

Varying the motor speed has no effect on perfect pulse timing.

Boncuk