You doing a great tested and modified the values of resistors, nice.

R2 changed from 1.2K to 15K, that is no harm for the circuit, since no any heat for all resistors, did you touch the leds to sense the temperature?

If you could then you can test the current of leds.
The method one is just in series the current meter(set to 200 mA) into the leds circuit, another method is in series with a 1 Ω to the leds circuit, and measuring the voltage of 1 Ω using the voltage meter, and calculate I = V/1 Ω, that is the current of leds.

The below is the new circuit for your another application that it was improved for the circuit in #17, I was used the same output driver to drive the leds from my first own designed in #13, this one should be have no the toggle problem, but you still can adjust the values of resistors to match what you want.

 

did you touch the leds to sense the temperature?

No I did not. I will leave modified circuit #13 on for 15 mins and touch leds for temperature. I have high hopes/expectations on this! ...

Should I use higher 1/2 or 1 WATT resistors for either of these circuits? You have (1) 1/2 watt resistor labeled on circuit in post #13. But only 1/4 watt resistors in circuit on post #21.

The below is the new circuit for your another application that it was improved for the circuit in #17,

I will try this circuit tonight as well and report back. Thank you so much for your assistance!

TONY

 

The circuit in #13 has voltage divider problem, this new circuit has no that problem, I calculated the current used standard method, but you still can adjust the values of R2 to match what you need as your posted in #20.

 

The circuit in #13 has voltage divider problem, this new circuit has no that problem, I calculated the current used standard method, but you still can adjust the values of R2 to match what you need as your posted in #20.

Thank you ScottWang. I will test this circuit out tonight. I need to first buy 1n4148 diodes.

TONY

 

Thank you ScottWang. I will test this circuit out tonight. I need to first buy 1n4148 diodes.

TONY

If you already have the 1N4004 in hand then you can use it to try or even use it is ok.

 

Hi ScottWang

I tried both circuits tonight on my breadboard.

Circuit in post #23, Positive triggered, works great. R2=1.5k ohms did get a little warm after 10 mins. All other components remained cool. I increased R2=4.7k ohms. Circuit worked fine and remained cool! ... Thank you!

I then tried Circuit in post #21. Ground triggered. That circuit did not work well. ... Output LED did remain lit till input Ground was triggered. ... However, the Input was always emitting a ground. Enough to have LED lit bright from input. After a few times of pulsing the input to straight ground. The 2n3904 burnt out. I tried this twice.

TONY

 

About the circuit in #21. (I forgot to modify the values of watt for R3, it can't be 1/4W)

Ib1 = the base current(Ib) of Q1, Ic1 = the collector current(Ic) of Q1.
Vbe2 = 0.7V, the voltage between base and emitter of Q2, when base current flows out and turn on Vbe.
Vce1 = 0.2V, the voltage between collector and emitter of Q1 when c,e get into the saturation region.

Ib1 = (12V-Vbe1)/R1
= (12V-0.7V)/10K
= 11.3V/10K
= 1.13 mA

Ic1 = ((12V-Vce1)/R2) + ((12V-Vbe2-Vce1)/R3)
= ((12V-0.2V)/10K) + ((12V-0.7V-0.2V)/1.5K)
= (11.8V/10K) + (11.9V/1.5K)
= 1.18 mA + 7.93 mA
= 9.11 mA

So you can see the Ib1=1.13 mA and Ic1 = 9.11 mA, there is no reasonable reason to damage the 2N3904.

Please take R1, R2, R3 away from the breadboard and using multi-meter K range to measure them to make sure the real values match with the printed colors, specially the value of R1.

If you have some other parts then use those to try.

 

The circuit in #21, I added R2(1K) to protect the input when it has any positive voltage cross on Vbe.

 

Thank you Scott. I did comfirm breadboard resistor values with post #21. All was ok.

I will try this new circuit in post #28 this evening. I am very excited to get this circuit going .... I will report findings. Thank you.


Tony

 

You said the 2n3904 was burnt out tn the post #26, did you find out anything wrong?

 

You said the 2n3904 was burnt out tn the post #26, did you find out anything wrong?

I found nothing wrong. All resistor values were same as your circuit called out. (2) 2n3904 did fail.

Tony

 

ScottWang

I tested the circuit in post #28. I have attached photos of my breadboard. You will notice I have a Red LED on the Input for visible feedback. This is how noticed the 2n3904 was emitting Ground. I kept increasing the value of R2 to 100k. At 100k the Red LED was fully out and a Ground to the of BASE triggered the circuit correctly. ... I also removed R1 with R2 at 100k. The Red LED became Dim. ... So here are my findings.

With R2=1k and R1 in place. Red LED full bright.
With R2=100k and R1 in place. Red LED off.
With R2=100k and R1 missing/omitted. Red LED Dim.

With R2=100k and R1 in place. I tried this circuit with the proper Output LED. No components got warm and ALL was good!

Tony

 

With R2=1k and R1 in place. Red LED full bright.

That's all worked as designed, did you feel any resistor get warm?

The practical wattage with the calculation values of resistor:
At least three times of calculation values, maybe it will get a little warm.
If using five times of calculation values then it should be no warm or just a tiny.

With R2=100k and R1 in place. Red LED off.

What I designed was the normal bjt switch and it working in the saturation region, it can be works over 10Khz and could match the most of applications, no need to change the resistors.

When R2=100K then the bjt will be working in the linear region as a amplifier, if the load is change then the resistor also need to change.

I just tell you that their difference, so don't worry your changed when they are working fine.

With R2=100k and R1 missing/omitted. Red LED Dim.

When the input was floating then the base will be catching the noise as 60hz from the air and the bjt is working in the linear region, so the output current will be as Ic1 = Ib1*hfe.

With R2=100k and R1 in place. I tried this circuit with the proper Output LED. No components got warm and ALL was good!

The reason that I already mentioned in the above, if you don't want to change the resistor then you have to change the load, the best results are the circuit working fine and no components get warm, nice done.

 

ScottWang

No components got warm during testing.

If I understand you correctly. R2 at 1k is fine. No need to increase 2 value. ... But increasing R2 value is not a bad thing. Correct?

I like your circuit here. It is different than my circuit 2 in post #1.

Thank you ScottWang.

TONY

 

If I understand you correctly. R2 at 1k is fine. No need to increase 2 value. ... But increasing R2 value is not a bad thing. Correct?

Yes.
Because the working frequency is low and you can accept the brightness, so increasing the values of R2 is a good thing.

 

Yes.
Because the working frequency is low and you can accept the brightness, so increasing the values of R2 is a good thing.

EXCELLENT!!! I will increase R2 value to 100k ohms for my visual satisfaction ... Thank you ScottWang for your assitance!!! Thank you ... thank you!!!

TONY

 

EXCELLENT!!! I will increase R2 value to 100k ohms for my visual satisfaction ... Thank you ScottWang for your assitance!!! Thank you ... thank you!!!

TONY

You are welcome ...

 

ScottWang

Should I use 1/4 watt or 1/2 watt resistors? I tested with 1/4 watt and no components became warm after 15 minutes. As of now, I going 1/4 watt.

Tony

 

When the resistor no any warm then using 1/4W is ok, if a little warm then using 1/2W or higher.