I just finished a scratchbuilt turnatable and have used a decoder to power it and the MRC auto reverser to handle the polarity thing. Now instead of an indexing device I would like to have a light come on when the TT track is lined up with its leads. Any suggestions will be welcome. I was kinda looking for a simple contact on the TT to turn on the light, or perhaps at dwarf signal at each lead that comes on when the track is alined. Prototype usage is not necessarily required.
How about having the light light up when the turntable isn't moving? Would that work for you?
How many volts are you running through your turntable motor?
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
Without seeing the application I would suggest as a possible solution using a roller lever switch mounted so that it would be tripped when the tracks align. Another option would be to use an infrared detector circuit which might be more precise and easier to initially setup and adjust.
Just throwing ideas around.
reklein wrote:The TT motor is on 12 V from the decoder. I need the light to light up when the tracks are alined.
I think it's safe to assume that if the table isn't moving it's going to be aligned with some track. So I think this circuit is what you are looking for. It's about $1 in parts. 6 cents for the NPN transistor. 50 cents for the Full bridge rectifier, and about 40 cents in resistors and lights.
reklein wrote:Nope,sorry. The turntable at this stage has no indexing whatsoever. You control the rotation of the table using the the digitrax throttle and it will rotate until you turn off the throttle. You align the tracks by eye. I want a light to come on when the tracks align. I'm thinking of an LED at each lead track that will light when a contact on the TT touches the leads to the LED. I need a stop distance of +/- 1/32".
oh...tricky...
Idea #1:
Just my suggestion but maybe you could use a tomar shoe (bronze phosphur on the bottom of the turntable. You could then paint a line about 1/64" wide using conductive paint in the turntable pit to complete the circuit. This would be the least favored way as you would have to line the paint up carefully...and I mean carefully. You would also have to narrow the shoe to 1/64" wide.
Idea #2:
Line up the table using IRDOT sensors or photovoltaic cells. This would require some electronics knowlege. But upshot is you can adjust the placement of the sensor. AND you could get the circuit to cut the power to the table once it lines up! Sort of like a stepper motor.
Hello,
Search Turntable Drive. You will see the Geneva Drive that I built. One Micro switch can be added that will trigger a light when the bridge is lined up. The Geneva Drive is very accurate. it is used to transport movie film. Hope this helps ypur friend.
Jerry
You could also use one uv emitter and detectors for each track. Make the output and input very small to maximize allignment.
I think RR Mel has figured out how to align the tracks with IR and no visible indicators. Find one of his posts and follow his sig line to his website.
Henry
COB Potomac & Northern
Shenandoah Valley
Hopefully, the OP has found a solution sometime during the last 13 years since he first posted his question.
Rich
Alton Junction
I got sucked into a necro thread? Oh the shame!