Separate Brake Light From Turn Signal

[ThomsCircuit]

Looks like U1A/B pin numbers are incorrect on your schematic(s).

Well the condition is no longer an issue but the output does not respond. I just don't think I have this bread boarded correctly. I have tried for hours and I just get confused on how to convey the schematic to the BB.

Ill post a few pictures and some voltages. Any additional help is appreciated I feel defeated but I won't give up on this.

 

[eTech]

Hi

So...it is best to separate the circuit into functional blocks for troubleshooting.
See the schematic below.

The jumper symbols J1-J7 are not jumpers, but represent where one functional block begins and ends. The symbols are points in the circuit that can be opened to separate each block and test it independently from the other blocks. I recommend to start testing at the Left Blink input, and once it is working, move to the next block on the left and test. This is "divide and conquer" approach to troubleshooting.

So...as a simple example, to test the "Left Blink Input" block:
1. Disconnect LTR wire from Q3-collector while leaving R12 connected to Q3-C.
Then apply 12v supply power to the circuit.
2. Check the voltage at Q3-Collector.
2A. With ~0V volts at "LTB" input, the voltage at Q3-C should be ~ +12V.
2B. With ~+12V volts at "LTB" input, the voltage at Q3-C should be ~ 0V.
If "Left Blink Input" block passes these tests, it works, then move to the next block.

For testing purposes, ~0V means less than 500mV.

Testing in this manner will allow you to identify the problem.

Ask questions if you need to...we'll help to get it working.

 

[eTech]

Well the condition is no longer an issue but the output does not respond. I just don't think I have this bread boarded correctly. I have tried for hours and I just get confused on how to convey the schematic to the BB.

Ill post a few pictures and some voltages. Any additional help is appreciated I feel defeated but I won't give up on this.

View attachment 147302

View attachment 147303

View attachment 147304

Can you post a good picture of the top view of the breadboard please?
Its kinda hard to see the connections and trace wires with the pictures you posted.

 

[ThomsCircuit]

Voltage readings.

Can you post a good picture of the top view of the breadboard please?
Its kinda hard to see the connections and trace wires with the pictures you posted.

 

[ThomsCircuit]

1. Disconnect LTR wire from Q3-collector while leaving R12 connected to Q3-C.
Then apply 12v supply power to the circuit.
2. Check the voltage at Q3-Collector.
2A. With ~0V volts at "LTB" input, the voltage at Q3-C should be ~ +12V.
2B. With ~+12V volts at "LTB" input, the voltage at Q3-C should be ~ 0V.
If "Left Blink Input" block passes these tests, it works, then move to the next block.

both LTB & RTB collectors work as expected.

 

[ThomsCircuit]

junction (6) fails 12v no power applied / only drops to 7v with power applied.
Isolate 4048 from 1453. 4048 passes test. 1453 fails test
EDIT:
junction 1 & 2 work
junction (3) works
Junction (4) stays high regardless of input
Junction (5) stays high regardless of input
junction (6) works
junction (7) stays high regardless of input

 

[ThomsCircuit]

additional views

 

[eTech]

junction (6) fails 12v no power applied / only drops to 7v with power applied.
Isolate 4048 from 1453. 4048 passes test. 1453 fails test
EDIT:
junction 1 & 2 junction (3) works now
Junction (4) stays high regardless of input
Junction (5) stays high regardless of input
junction (6) ok
junction (7) stays high regardless of input

The "Left Blink Detector" is tested differently.
It is, basically, a one shot multi-vibrator and, when triggered, should produce a low (Qbar=0V) output pulse for about 2.5 seconds. The one shot is triggered when the voltage at U1A-B(P5) falls from +12V to 0V.

Since we now know the "Left Blink Input" block is working, reconnect the LTR wire as shown in the schematic. Then, to test the "Left Blink Detector" function:

1. Apply power to circuit.
1A. Check the voltages at U1A-4,1,8. The voltage should be ~0V (ground)
1B. Check the voltages at U1A-3,16. The voltage should be ~+12V.
1C. These voltage measurements should not change and remain constant throughout the test.
2. Check the voltage at U1A-5.
2A. With ~0V volts at "LTB" input, the voltage at U1A-5 should be ~ +12V.
The voltage at U1A-7 should be ~12V.
2B. When ~+12V volts is applied at "LTB" input, the voltage at U1A-5 should be ~ 0V.
Simultaneously, the voltage at U1A-7 should fall to ~0V, remain at 0V for about 2.5 seconds, then rise to ~12V.

Report back.

 

[ThomsCircuit]

1. Apply power to circuit.
1A. Check the voltages at U1A-4,1,8. The voltage should be ~0V (ground)
1B. Check the voltages at U1A-3,16. The voltage should be ~+12V.
1C. These voltage measurements should not change and remain constant throughout the test.
2. Check the voltage at U1A-5.
2A. With ~0V volts at "LTB" input, the voltage at U1A-5 should be ~ +12V.
The voltage at U1A-7 should be ~12V.
2B. When ~+12V volts is applied at "LTB" input, the voltage at U1A-5 should be ~ 0V.
Simultaneously, the voltage at U1A-7 should fall to ~0V, remain at 0V for about 2.5 seconds, then rise to ~12V.

all worked as expected. I am applying constant 12v to LTB input to test U1A-5 then a slow blink so i can observe the rise and fall of U1A-7

 

[eTech]

OK..I will get back to you on how to test U2 functionality.

 

[ThomsCircuit]

OK..I will get back to you on how to test U2 functionality.

Thought I would mention there is a scenario where the output is somewhat successful. This is when both RTB and LTB are flashing in sync the output mirrors the inputs but every other flash/blink is a shorter dimmer version. So you get a strong blink followed by a weak blink. If I speed up the rate It is less noticeable.

 

[eTech]

OK..I will get back to you on how to test U2 functionality.

U2 provides an OR/AND combinational logic function.
Inputs A,B are two inputs of one OR gate inside U2.
Inputs E,F are two inputs of a second OR gate inside U2.
The outputs of the two OR gates are "ANDed" together inside U2.
The logic is:
If (A OR B) AND (E OR F) are at +12v, then "J" should produce +12V
If (A AND B) OR (E AND F) are at 0v, then "J" should produce 0V.

To test this function, remove the connections to pins U1-5,6,13,14,
then temporarily connect these pins to 0V (ground). Pins U1-5,6,13,14
will be called the "input pins" from here on for testing purposes.
1. Apply power to circuit.
1A. Check the voltages at pins U2-3,4,8,9,10,11,12,15. Each pin voltage should be ~0V (ground)
1B. Check the voltages at pins U2-2,7,16. Each pin voltage should be +12V.
1C. These voltage measurements should remain constant throughout this test.
2. Check the voltage at U2-1.
2A. With 0V volts at ALL input pins, the voltage at U2-1 should be 0V.
2B. When +12V volts is applied to U1-14, the voltage at U2-1 should be 0V.
2C. When +12V volts is applied to both U1-14 AND U1-6, the voltage at U2-1 should be +12V.
3. Re-Check the voltage at U2-1.
3A. With 0V volts at all input pins, the voltage at U2-1 should be 0V.
3B. When +12V volts is applied to U1-13, the voltage at U2-1 should be 0V.
3C. When +12V volts is applied to both U1-13 AND U1-5, the voltage at U2-1 should be +12V.

The Mosfet DRIVER test:
Mosfet M1 should be normally off. R4 ensures this by pulling up M1's gate to +12v.
Anytime M1 has +12v at its gate pin, M1 should be off, and the Brake Light should be off.
Anytime M1 has 0v at its gate pin, M1 should be on, and the Brake Light should be on.

 

[eTech]

Thought I would mention there is a scenario where the output is somewhat successful. This is when both RTB and LTB are flashing in sync the output mirrors the inputs but every other flash/blink is a shorter dimmer version. So you get a strong blink followed by a weak blink. If I speed up the rate It is less noticeable.

OK. we will need to "tune" the CD14538 after we're finished testing and sure the circuit is working correctly.

 

[ThomsCircuit]

OK. we will need to "tune" the CD14538 after we're finished testing and sure the circuit is working correctly.

I will have to put this on hold for a few days. We just finished cleaning up after Helene and now we must brace ourselves for Milton.

 

[eTech]

I will have to put this on hold for a few days. We just finished cleaning up after Helene and now we must brace ourselves for Milton.

OK....you and yours be safe..

 

[eTech]

Been trying to bread board and test the schematic from post #92.

T.B

Hi

Just letting you know I bread boarded the whole circuit in post #92, on 10/6, without the Shockley diodes because I didn't have them. I used a blink frequency of 0.5 Hz and it works as intended.

 

[ThomsCircuit]

Just letting you know I bread boarded the whole circuit in post #92, on 10/6, without the Shockley diodes because I didn't have them. I used a blink frequency of 0.5 Hz and it works as intended.

If you would be so kind to share some bread board photos and your 0.5 Hz blink schematic I might be able to see what I did differently or mis read the original schematic.

I noticed that your diagram uses IRF7406 while I use IRF5305. I show pin numbers but yours does not. Maybe there is a problem in how I connected mine.

 

[eTech]

If you would be so kind to share some bread board photos and your 0.5 Hz blink schematic I might be able to see what I did differently or mis read the original schematic.

See Below:

I noticed that your diagram uses IRF7406 while I use IRF5305. I show pin numbers but yours does not. Maybe there is a problem in how I connected mine.

I used an FQP7P06 PMOS mosfet, but that wouldn't affect the timing the way you described.
I would suspect the circuit around the CD14538. In my circuit, I used 240K resistors, 10uf tantalum caps, and 1N4148 diodes for the timing components. All these are identical types/tolerance, etc.
I don't have C2/C11 installed as those are for noise and I'm using a Signal generator as a flasher.
What are you using for a flasher?

 

[ThomsCircuit]

What are you using for a flasher?

I adjust the pot to match my trucks turn signal rate of 85 cycles per minute

 

[eTech]

I adjust the pot to match my trucks turn signal rate of 85 cycles per minuteView attachment 147361

I'm using a BK prescision waveform generator to produce a flash signal. I can set the duty cycle independent from the frequency. I checked the circuit at 0.705 Hz, 50%DC and it works fine.

I think the short flash is cause by the 555 astable not producing 50% duty cycle. "duty cycle" is the percentage of time the output is high vs output low. The 555 cannot produce 50% duty but can come close. The problem with the 555 circuit you have is the duty cycle will change whenever the frequency changes.
85 Flashes per minute is 0.705 Hz. If C1 is 10uF, R2 is 1K, then R1 (or pot) should be 100K. That sets the frequency to about 718milliHz and 50.25% duty cycle (close enough).

Does your truck's flasher lights look to flash equal time on/off?