bore da Allison,
As already pointed out, as the White LED require approx 3.2V forward voltage drop, you cannot drive 4 in series from 12V, use two pairs in parallel.
E

Diolch yn fawr Eric

What do you think of the Circuit proposed by 'AnalogKid post #58 ??


Allison

If you have other parts, the circuit can be adapted. NPN's such as 2N4401, 3904, 2222, etc? PNP's such as 2N4403, 3906, 2907, etc? Logic chips: 74xx14, 00, 02, 32, etc? 555: do you have bipolar (LM555, NE555) or CMOS (LMC555, etc.)? I probably can do it with a 555 version with a PNP transistor if you have those parts already.

1. Can you expand on the timing between the two SENSE signals? As I understand things, both SENSE signals go low when triggered by an object, and S2 always is triggered *after* S1. Is this correct?

2. If so, then does S1 release (return high) always *after* the timer has finished its 10-30 second interval, *always* before, or sometimes either one?

3. If S2 has been triggered, does it return high *always* before the next triggering of S1? Or might S1 go low again while S2 still is low?

4. Does the POINT switch have to switch 12 V, or can it be connected to GND?

5. If the number of white LEDs can be reduced from 4 to 3, or increased to 6, things happen.

Depending on what the signals do and what parts you have, there are lotsa combinations that will work.

ak

Hi,

Would the following adaptation of your circuit diagram work ?

 

Close, but ...

You have the 555 powered by the +12, but the inputs go up to 5 V only. This might not be high enough for correct circuit action. And, the IR module might not like having 12 V impressed on its output pins. Yes, the LM393 chip it uses can stand it, but we don't know if the output has a pull-up resistor than might backfeed the external 12 V to its input circuit.

Also, in the "rest" case (S1 and S2 both high), the 555 output is low and the green (and white) LEDs are off, This does not agree with post #43, and is one of the reasons I moved away from the 555. Of course there is a way to make it work. Do you have any small PNP transistors?

If it were me (but my skill set probably is a bit above yours), I'd check an IR module to see if the output has a pull-up resistor, and remove it if so. This gives a true open-collector output, so the module can be powered by 5 V (to assure proper operation of its IR parts), but drive a 12 V-powered 555 (or whatever) correctly. Just sayin ...

ak

 

You have the 555 powered by the +12, but the inputs go up to 5 V only. This might not be high enough for correct circuit action. And, the IR module might not like having 12 V impressed on its output pins. Yes, the LM393 chip it uses can stand it, but we don't know if the output has a pull-up resistor than might backfeed the external 12 V to its input circuit.

Also, in the "rest" case (S1 and S2 both high), the 555 output is low and the green (and white) LEDs are off, This does not agree with post #43, and is one of the reasons I moved away from the 555. Of course there is a way to make it work. Do you have any small PNP transistors?

ak

I can get hold of some small PNP transistors, but is this any better



Kindest
Allison

 

Solves the input issue. What about the output? Can you make a little truth table with all of the LED combinations? It might be that the circuit is fine and I don't understand the requirements.

ak

 

Solves the input issue. What about the output? Can you make a little truth table with all of the LED combinations? It might be that the circuit is fine and I don't understand the requirements.

ak

Truth Table

Stage	Condition	RED	GREEN	WHITE
A	Train Triggers Sensor 1 and the Timer is Started	YES	NO	NO
B	Pre-Set Time Elapse (J1 = C2) or Train Triggers Sensor 2 (J1 = C1), Points Not-Switched	NO	YES	NO
C	Pre-Set Time Elapse (J1 = C2) or Train Triggers Sensor 2 (J1 = C1), Points Switched	NO	YES	YES

Hope this helps....



Allison

 

Before Stage A, when the system is powered up and just sitting, is that the same as after B or C (green and maybe white)?

Based on this table, take another look at the 555 output in #63. Remember that the 2N7000 is configured as an inverter.

ak

 

Before Stage A, when the system is powered up and just sitting, is that the same as after B or C (green and maybe white)?

Based on this table, take another look at the 555 output in #63. Remember that the 2N7000 is configured as an inverter.

ak

On start up there will be no Trains running so it will be as either B or C depending on the position of the points. Not sure what i am supposed to be looking at in #63, sorry im still a novice.

Allison

 

During the timing period, the 555 output is high, which turns on the transistor, which lights the green and white LEDs. In the rest state, the 555 output is low, the transistor (Reference Designator: Q1) is off, and the red LED is on. This does not agree with your table, which makes any 555-based solution a bit harder.

One solution is a second transistor (Q2) to invert the 555 output. Another is a bit more complex to describe, but the result still is 2 transistors instead of just one. One way to judge the complexity of competing approaches, especially for home-built circuits (as opposed to production line assembly) is to count the number of components, and the total number of *soldered* pins; not the interconnecting wires, just the pins.

Yardwork calls. More later.

ak

 

During the timing period, the 555 output is high, which turns on the transistor, which lights the green and white LEDs. In the rest state, the 555 output is low, the transistor (Reference Designator: Q1) is off, and the red LED is on. This does not agree with your table, which makes any 555-based solution a bit harder.

One solution is a second transistor (Q2) to invert the 555 output. Another is a bit more complex to describe, but the result still is 2 transistors instead of just one. One way to judge the complexity of competing approaches, especially for home-built circuits (as opposed to production line assembly) is to count the number of components, and the total number of *soldered* pins; not the interconnecting wires, just the pins.

Yardwork calls. More later.

ak

When you get moment could you tell me what i need to do (with a circuit diagram would be nice), to make it work as i need

kindest
Allison

 

When you get moment could you tell me what i need to do (with a circuit diagram would be nice), to make it work as i need

Circuit #57 does exactly what you describe. If you really want to use 555's, I'll post something later today. Clear skys, 90 degF, yard work.

You obviously have excellent panel wiring talent. What is your skill set for assembling small circuits on perf board, and maybe removing a surface mount part from each IR module?

ak

 

Circuit #57 does exactly what you describe. If you really want to use 555's, I'll post something later today. Clear skys, 90 degF, yard work.

You obviously have excellent panel wiring talent. What is your skill set for assembling small circuits on perf board, and maybe removing a surface mount part from each IR module?

ak

A lot depends on how small the component is.....

Allison

 

hi A,
Look at this timing diagram.
E

 

Trying to eliminate parts. Is it ever possible that, after SENSE-1 goes low to trigger the 555 timing period, SENSE-1 still will be low after 30 seconds; after the end of the longest timing period?

ak

 

hi A,
Look at this timing diagram.
E

Hi Eric,

Looks good to me,
Will incorporate into my diagram and then let you have a look to make sure ive understood it correctly

kindest
Allison

 

Look at this timing diagram.

According to your diagram, after Sensor1 spikes low, Red goes off. In post #65 Stage A, after the train triggers Sensor 1, Red is on.

ak

 

Here is a first pass at a 555 version. this one has zero external transistors, but I had to add two diodes.

The LMC555 can sink 50 mA, and the worst-case total LED current is 30 mA, so that should be ok. The problem is when the 555 is high during the timing period. If the white LED Vf is 3.5 V and the 555 output is 4.5 V, that totals 11.5 V which means that the white LED will not be off. Two small power rectifiers in series adds about 1.4 V of drop to the string. Now there must be 8.4 V *above* the 555 output voltage for the white LEDs to come on, and there is only 7.5 V available (12 -4.5).

This should work, but I welcome any and all analysis. One way to get rid of D7 and D8 (and still have even more operating margin) is to increase the white LED strings to three LEDs each.

Still waiting to hear about SENSE-1 vs the 555 time period; that could eliminate two more parts.

ak

 

About #76 ...

Even with the two additional diodes, this circuit might have some issues. At 30 mA in rest mode with the point switch closed, the CMOS 555 low output voltage might not be low enough to cutoff current to D1. Plus, with D1 and D2 powered by 5 V, the difference between the D2 Vf and the D1+D3 Vf equates to about 1.4 mA less current through D1 than D2, assuming the U1 output is 0 V. This is enough to matter. I'm leaning back toward the #57 schematic with the CD4093. It is only one more soldered pin and the D1 - D2 part is much better behaved. The difference in current is only 7%.

Speaking of #57, I added a discharge diode (D8) around the timing network. This discharges C1 in under 0.1 s.

ak

 

hi A,
Look at this timing diagram.
E

Hi Eric,

What do you think of this diagram... ive put it in to a format i could build on to breadboard.



Kindest
Allison

 

hi Alllison,
Is the 555 Reset pin Open,, and the Sense 1 and 2 to Trigger correct.?
E

Update:
When would you expect the Point Sw to be operated, timewise, with respect to say to Sense2 being triggered.?

 

hi Alllison,
Is the 555 Reset pin Open,, and the Sense 1 and 2 to Trigger correct.?
E

Update:
When would you expect the Point Sw to be operated, timewise, with respect to say to Sense2 being triggered.?

Hi,

The Point can be switched at any time, as this would be set as a route control operation... where as the Red & Green are operated by the actual passage of the train.

The only time that the Red & Green would be manually operated are 1) a RED signal is required to hold the train at a station. not very often, 2) a GREEN signal to reverse the RED state.

kindest
Allison