Help me with LED Strobes

[vne147]

Boncuk,

I haven't worked a lot with triacs either. I actually only used them a few times and that was all in 110 VAC applications. I kind of assumed that I could find one rated for the current/voltage requirements of this circuit. Maybe that's not the case. I just know that for the 555 timer to work properly, current has to flow both ways through the timing resistor. That's why I picked the triac. If the triac idea ended up not working the same thing could probably be accomplished with 2 transistors in parallel and their polarities reversed. The method you discussed using the motor is simpler than my idea but the original poster mentioned a 555 and a 4017. That's why I went down that path.

 

[Ubergeek63]

OK... take the previous schematic: https://www.electro-tech-online.com/attachments/sos-jpg.23392/

Replace the 555 circuit with the standard astable circuit from the data sheet set up for the dash on time and the space off time.

The diodes then go to a resistor to pin 7 to set up the dot on time.

The 555 output of the 555 going to the 4017 the also drives your LED with the morse sos code sequence.

 

[Boncuk]

Boncuk,

I haven't worked a lot with triacs either. I actually only used them a few times and that was all in 110 VAC applications. I kind of assumed that I could find one rated for the current/voltage requirements of this circuit. Maybe that's not the case. I just know that for the 555 timer to work properly, current has to flow both ways through the timing resistor. That's why I picked the triac. If the triac idea ended up not working the same thing could probably be accomplished with 2 transistors in parallel and their polarities reversed. The method you discussed using the motor is simpler than my idea but the original poster mentioned a 555 and a 4017. That's why I went down that path.

Hi vne147,

here is good example of low power triac (TO92 package): BR101 (50V, 100mA) or BRY55/200 (200V,800mA)

Boncuk

 

[Boncuk]

another alternative: Use an UJT (BRY56)

 

[vne147]

OK... take the previous schematic: https://www.electro-tech-online.com/attachments/sos-jpg.23392/

Replace the 555 circuit with the standard astable circuit from the data sheet set up for the dash on time and the space off time.

The diodes then go to a resistor to pin 7 to set up the dot on time.

The 555 output of the 555 going to the 4017 the also drives your LED with the morse sos code sequence.

OK, I think I understand now. Is this what you are describing? In the schematic R3 and R5 would have the same value and R4 would be higher. That should produce the "... --- ..." pattern. Also, can you please explain what you meant by SCR limitations and why the triac idea won't work? I would like to understand why using the triac is a bad idea. Thanks.

 

[delokaver]

hi boncuk,

can i replace this triac with a mosfet ?? P chanel mosfet posibly ??

 

[vne147]

hi boncuk,

can i replace this triac with a mosfet ?? P chanel mosfet posibly ??

Delokaver,

You don't need the triac at all anymore. The modification suggested by Ubergeek completely eliminates it. See the schematic attached to my previous post. If you are planning on building this thing, I would highly encourage you prototype it first to ensure it works as expected. I didn't actually test any of this. The value of R2 will set the off time or time in between pulses. The value of R3, R4 and R5 will set the on time or the time the led is lit. R3 and R5 should be equal value and R4 should be a higher value than them to make the middle three pulses longer. Another improvement could be made if you join the wires coming out of D2 and D4 before the resistor, you can use a single resistor in place of R3 and R5. That way both of the ... portions of the SOS signal will be equal and not slighlty different due to individual variations in resistor values. Whether or not that would be noticable is questionabe.

 

[Ubergeek63]

Boncuk,

I haven't worked a lot with triacs either. I actually only used them a few times and that was all in 110 VAC applications. I kind of assumed that I could find one rated for the current/voltage requirements of this circuit. Maybe that's not the case. I just know that for the 555 timer to work properly, current has to flow both ways through the timing resistor. That's why I picked the triac. If the triac idea ended up not working the same thing could probably be accomplished with 2 transistors in parallel and their polarities reversed. The method you discussed using the motor is simpler than my idea but the original poster mentioned a 555 and a 4017. That's why I went down that path.

The current has to flow both ways in the capacitor. It is charged through the resistor and discharged through the... get this... discharge pin.

Triacs require a minimum trigger current to fire and a minimum holding current below which they turn off, both of which are less than the capacitor charging current in a 555 circuit (generally 5-50mA to fire and 100-200mA to stay on.

To have a chance of using a thyristor you would need to use a PUT, however since it always charges from the positive rail, all you need is diodes from the 4017 pins that are for the short flashes.

 

[Ubergeek63]

The value of R3, R4 and R5 will set the on time or the time the led is lit. R3 and R5 should be equal value and R4 should be a higher value than them to make the middle three pulses longer. Another improvement could be made if you join the wires coming out of D2 and D4 before the resistor, you can use a single resistor in place of R3 and R5. That way both of the ... portions of the SOS signal will be equal and not slighlty different due to individual variations in resistor values. Whether or not that would be noticable is questionabe.

Actually I was suggesting a resistor from pin 7 to VCC ... Oh hell....

R8 sets off time, R7 sets dash time, R3 sets dot time. Tying the output LED to Q9 gives you a pause. There might be an artifact during the pause...I did not think it through fully.

Dan

 

[delokaver]

please review

Delokaver,

You don't need the triac at all anymore. The modification suggested by Ubergeek completely eliminates it. See the schematic attached to my previous post. If you are planning on building this thing, I would highly encourage you prototype it first to ensure it works as expected. I didn't actually test any of this. The value of R2 will set the off time or time in between pulses. The value of R3, R4 and R5 will set the on time or the time the led is lit. R3 and R5 should be equal value and R4 should be a higher value than them to make the middle three pulses longer. Another improvement could be made if you join the wires coming out of D2 and D4 before the resistor, you can use a single resistor in place of R3 and R5. That way both of the ... portions of the SOS signal will be equal and not slighlty different due to individual variations in resistor values. Whether or not that would be noticable is questionabe.

hi vne147,

i draw the schematic as per your last post, please let me know if this already same with what you means.

also i am still can not calculation the vallue for some componen, res and the cap, could you please take a look with detail and correct me ???

 

[vne147]

OK, I guess I misunderstood again. However, I don't see why the way I had it wouldn't work, do you? The 4017 output pins should be at the supply voltage when high. In theory the 555 shouldn't care if it gets the voltage from Vcc or from the 4017.

 

[Boncuk]

OK, I guess I misunderstood again. However, I don't see why the way I had it wouldn't work, do you? The 4017 output pins should be at the supply voltage when high. In theory the 555 shouldn't care if it gets the voltage from Vcc or from the 4017.

If you use a CMOS version of the 555 it won't care. The normal version cares a lot. A 4017 is limited to about 10mA at 9V. It can't possible supply an IC putting out 200mA.

 

[vne147]

If you use a CMOS version of the 555 it won't care. The normal version cares a lot. A 4017 is limited to about 10mA at 9V. It can't possible supply an IC putting out 200mA.

I'm not using the output of the 4017 as the supply voltage and current source for the 555, I'm just using it as the current source into pin 7. That should require less than 1 mA. My point was that the 4017 output pin voltage should be the same as supply voltage so the 555 shouldn't care if the resistor that is on pin 7 in connected directly to supply voltage or to the output of the 4017.

 

[Boncuk]

I'm not using the output of the 4017 as the supply voltage and current source for the 555, I'm just using it as the current source into pin 7. That should require less than 1 mA. My point was that the 4017 output pin voltage should be the same as supply voltage so the 555 shouldn't care if the resistor that is on pin 7 in connected directly to supply voltage or to the output of the 4017.

Just consider the current flow of a low output forced high without current limitation.

 

[vne147]

Just consider the current flow of a low output forced high without current limitation.

Which low output is forced high without current limitation? If you're reffering to pin 7 on the 555 then I'm confused because there is current limitation. R3, R4 and R5.

 

[Boncuk]

Which low output is forced high without current limitation? If you're reffering to pin 7 on the 555 then I'm confused because there is current limitation. R3, R4 and R5.

Sorry, slight misunderstanding here. However the timer circuit doesn't oscillate in the simulation.

Ignoring the circuitry from outputs 0,1 and 2 of IC3 (meaning leave it connected) and connecting a 10K resistor beween pin7 and VCC the oscillator works.

Boncuk

 

[vne147]

hi vne147,

i draw the schematic as per your last post, please let me know if this already same with what you means.

also i am still can not calculation the vallue for some componen, res and the cap, could you please take a look with detail and correct me ???

Delokaver,

It will take me a few days to check over your schematic and give you values.

 

[delokaver]

hi vne147,

sure no problem at all, thank for your help friends