IR or Optical Sensors

Hi Stan,

After many new activities I am back.

First to the activities for any that may be interested:

1) My neighbor and good friend is a mechanical genius. He came up with a design for a new turntable to replace my very old one (which was a 22" dia. unit driven by a dc motor with a rubber drive turning a 24" wood disc. We tried to make it work by using a stepper motor with belt drive (instead of the original drive mechanism) controlled by an Arduino. This worked but didn't have the repeatability accuracy. So he came up with a totally new design using a lazy susan and slip ring combination, driven by a larger stepper motor with Arduino control. I will post details and code if any interest. Unfortunately, the motor mount was custom-made with his 3-D printer, but the total cost of parts was less than $100.

2) He then got more into the hobby when I explained my concern with the crossing gate and approach signals/accessories being energized for too long (burning up solenoids). So he completely designed and printed (3-D printer again) a crossing gate with flashing LEDs on the cross and gate, and operated with a tiny servo motor (no burn up). We both came up with an Arduino code version to operate the gate. I made a simple mock-up model of same and could post a video of the code in action. Took me long time to learn enough C language to write the program.

This brings me to the question (sorry if the above is of no interest or in the wrong area).  With the new gate design, we want to incorporate audio. Back many posts ago you presented your design using a modified MP3 player & audio amp. About a month ago, I bought the only cheap MP3 player available on ebay. Mine has a display and the circuit configuration is somewhat different than the one you modified. As such, I am posting pics of mine and would very much appreciated help in where to place the added capacitor. I will also check the audio amp I bought and see if it is same or different.

Thanks for any help.

Ken

ken's trains posted:

...

This brings me to the question (sorry if the above is of no interest or in the wrong area).  With the new gate design, we want to incorporate audio. Back many posts ago you presented your design using a modified MP3 player & audio amp. About a month ago, I bought the only cheap MP3 player available on ebay. Mine has a display and the circuit configuration is somewhat different than the one you modified. As such, I am posting pics of mine and would very much appreciated help in where to place the added capacitor. I will also check the audio amp I bought and see if it is same or different...

I see hundreds of choices on eBay including the 99 cent free-shipping version I've used but pink - 10 cents more if you want a black case.    

Yours seems to be going for $1.79 free-shipping in black.  All this high-finance is pretty heady stuff!

I've not messed with the screen version.  But I'm sure we can figure something out.

But first if I can make a suggestion, start a new Electrical thread titled MP3 sound for crossing gate or something like that.  I think the existing thread title about IR and optical sensors might not draw in some guys that have sound related expertise.  Some additional info to include would be:

1. Identification/photo of the amplifier module you have

2. Exactly what circuit/voltage or trigger drives the sound - 5V DC, 12V DC, Accessory 14V AC voltage from a relay, etc.

3. Did you mess with the unit before dis-assembling it?  Specifically, the way I use these modules is to turn the power switch "on" to confirm that it automatically starts playing an MP3 "song" with no additional button-pressing.  For all I know the screen based version wants to interrogate you requiring menu navigation.  So did you load a single MP3 "song" such as a crossing gate MP3 sound onto the microSD card, then turn on the player, and confirm the song automatically starts thru the audio jack via some earbud headphones?  The battery must have been charged which is usually done via a mini or micro USB cable.

Hi Stan,

I have done as you suggested and moved this discussion to a new forum titled:

"MP3 Sound for Crossing Gate" as you had suggested. Also this is the audio amp module I purchased on ebay:

"DC 5V Mini Digital Amplifier Board Class D 2*3W USB Power PAM8403 Audio Module ".

See you at the other forum. I have done as you suggested and tried a few things.

Ken

HI all. Well after spending a year on 3D design and construction of a 24" turntable (TT), I need some more electrical help. I have posted the TT stuff under a different topic. Upon completion & installation of the TT, it became apparent that an engine could run into the TT pit when the TT track was not positioned with the entry track. Decided to use an across track optical sensor to detect engine near end of track and breaking beam would open relay controlling (isolated) track voltage. Long ago, Stan posted lots of circuits for configuring optical sensors. However, one of the diagrams showing how to connect an LED emitter/IR sensor combination to control a 5V relay does not work as shown. If I connect the (-) output of the sensor directly to the relay it does not trigger. If I put a 10K resistor on the (-) sensor output and connect to grd and then also connect the (-) sensor output to relay trigger, there is not enough current to fully trigger the relay. However, the sensor sensitivity is great. If I reduce the resistor value (had to come down to 500 ohms) to allow sufficient trigger current, the sensor sensitivity is terrible (need to be almost touching the emitter). Did not realize that was how sensor sensitivity was controlled. So, is the solution to use the sensor (with 10K limiting resistor) to trigger a transistor and use the transistor to trigger the relay??

If I am close, would really appreciate a circuit sketch showing values.

Ken

ken's trains posted:

...Long ago, Stan posted lots of circuits for configuring optical sensors. However, one of the diagrams showing how to connect an LED emitter/IR sensor combination to control a 5V relay does not work as shown...

So we're talking apples-apples I assume it's a diagram from this thread.  What's the date & time of the post with the diagram?

Hi Stan,

Well I'm really sorry, but it's been a lot longer than I remembered--tough to get old. A good date/time would be 4/9/15 & 10:22 PM (that was my re-post of your original design). As to my most recent questions, I have the single emitter/sensor combo working now--just followed your design of that time. But would still like to know if sensor sensitivity is controlled by current through the sensor--seems to be what I experienced. If that's the case, I guess that's why this only works with the transistor in the circuit and the sensor just providing a trigger for the transistor which provides sufficient current to trigger the relay?? [It seems that the only thing that should be happening is varying light intensities affecting how much the sensor turns on--not the opposite; but then I don't understand how phototransistors work].

Second question regarding your earlier (4 yrs ago) schematic: you have a resistor/capacitor combo in the circuit that provides a time delay. If I remove those 2 components and just connect the 1st 10k resistor to the transistor base (since I don't need a delay), will the circuit still work?

Lastly: I am using this setup across a section of track to prevent an engine from running off the end of the track into the turntable (TT) pit by shutting off power to that track when the beam is broken. However, I need to disable (or bypass) this function when the TT is aligned with the track (and no I can't easily monitor for TT/trk alignment--too few slipring wires available) to allow engine to enter TT. So, other than adding another relay to bypass the 'safety' function (controlled by a switch at the console), is there some way to modify your circuit to easily disable the 'beam break' from triggering the relay (with some command from the control console; an "Enable/Disable" switch)?

Again, thank you for all of your help, and I can't believe it's been 4 yrs. since I've been on this topic. Didn't realize the turntable design & construction had consumed so much time.

Ken

Stan, it's me again. This was my (one of) main confusion. In your 8/12/15 at 5:47pm post, you show 2 sensors in series with the output of the 2nd connected directly to the control terminal of a 5VDC relay. I get the relay to trigger with one sensor connected this way, but the relay is energized when the beam is not broken. This is my normal condition and not acceptable. I tried changing the H/L trigger jumper on the relay, but that didn't work since I don't have a ground with the beam unbroken. I tried removing the capacitor, 2nd 10k resistor & diode (since I don't need a delay), but the relay will not trigger (tried all combos of H/L jumper). In one of your posts you had a push button that you crossed out and said "replaced with sensors in series". However you did not mention whether or not when removing the PB, the connection from Vcc to transistor base through the 10k resistor was still required. I have not connected that 2nd 10k resistor from Vcc to base--is that the problem.
Please clarify.
Ken

I realize that most eBay relay modules available now have a jumper(s) to select either H or L level trigger.  But let's just assume the H "only" module as described in the original discussion from years ago.  Since you don't need time-delay capability, as you correctly concluded, you don't need to worry about the capacitor/transistor circuitry.

Since you want the relay to turn ON when the beam is broken, try the above circuit.  Here's the steps in order.

- apply 5V DC power to the relay module 

- insert a 1K to 5K resistor between +5V DC and IN1 trigger.  The relay should turn on.  The resistor applies a HIGH trigger.  You want to insert the largest resistor value that reliably fires the relay.  So start with, say, 1K which will surely fire the relay.  If that works,try 2K or 2.2K (whatever you have).  If that still works, try 4.7K or 5.1K (whatever you have).

- insert the IR phototransistor.  When the phototransistor is illuminated, its resistance becomes a few hundred Ohms or so.  This shunts all the current from the IN1 trigger input to ground and the relay turns off.  If you break the IR beam to the phototransistor, the phototransistor's resistance jumps up to thousands or millions of Ohms which effectively means it is taken out of the circuit and the relay triggers as if the phototransistor is not there.

ken's trains posted:

...

Lastly: I am using this setup across a section of track to prevent an engine from running off the end of the track into the turntable (TT) pit by shutting off power to that track when the beam is broken. However, I need to disable (or bypass) this function when the TT is aligned with the track (and no I can't easily monitor for TT/trk alignment--too few slipring wires available) to allow engine to enter TT. So, other than adding another relay to bypass the 'safety' function (controlled by a switch at the console), is there some way to modify your circuit to easily disable the 'beam break' from triggering the relay (with some command from the control console; an "Enable/Disable" switch)?

 

This reminds me of the "problem" of killing power to the approach tracks to either side of a lift-bridge.  The mechanism must remove track power if the bridge is up so your $1000 engine does not perform a swan-song dive into the abyss.  The most common method on OGR is to use a lever/hinge/leaf switch.  When the bridge lifts, the spring-loaded leaf pops out and power is removed to the last few feet of track before the bridge.

So for a TT, I'd think something similar could be used.  For example, you could have one leaf switch per spur.  A tab/nib/finger on the rotating TT "bridge" would press the lever of the switch when it is aligned to the spur.  The switch then provides track-power continuity to the last few feet of track feeding the TT.

But given the topic is optical sensors, I suppose you could have a phototransistor on each spur "aimed" toward the center of the TT.  The TT "bridge" would have one IR LED firing an IR beam.  When the TT is aligned to a particular spur, it activates the phototransistor which triggers the $1 relay module.  The relay then provides track-power continuity to the last few feet of track feeding the TT.

Having just a single IR LED on the rotating TT section should not require adding more slip-ring circuits.  That is, you could use AC track power to power the IR LED.  Simply rectify the AC to DC and use a resistor to limit the current to the IR LED.