Making a Automatic electronic end of record tonearm lifter Revisited

I posted on this topic quite some time ago and got sidetracked by a major move. Now I have my HiFi set back up and working and would like to continue the project. The turntable is a Thorens TD-124 with a SME tonearm. I am now using a techniques Safety Raiser. It works OK, but is not ideal. The main dilemma I have is space on the tone board for the lift device. So the little Fwend and Q-up lifters will not work due to the area required. The Safety Raiser just fits, but it is old and warn out and is becoming unreliable and glitchy.

I would like to fabricate a lifter that is controlled by optical or proximity sensors. Have been looking at mini linear motors on eBay and have found this one I think will work:

I would position it under the tone board and have a rod attached to the slider and passing up through a hole in the tone board that would lift the tone arm.

The way I would like it to function is this:

The lifter would start in the low position.
When the tonearm reaches the end of the lp the lifter should move to the high position and remain there.

When the tone arm is moved back to the start position the lifter should return to the low position.

This would be my first Arduino project. Any advice is welcome. I am mostly interested in learning what Arduino devices are appropriate. And is this linear motor controllable.

It seems to me that using a small servo would be simpler. It has all the electronics inside.

Have you measured how much force is needed to raise the arm? The lifting lever is probably very close to the hinge point so the force may be greater than you expect.

With a stepper motor you will also need some sort of stepper motor driver. There is also the question of whether the stepper motor in your link can be run against its physical end-stops without damage. If not you will need some limit switches to detect when the slider is at the extremes of motion.

You have not said whether you have the equipment needed to detect when the tone-arm is at the end or start position.

An interesting project.

...R

Can You renovate the old Safety Raiser? What is wrong with it? What makes it unreliable? Is it the mechanical or the electrical part making it unreliable? Can that be repaired?

I like the idea of a screw gear but I’d use a geared-down DC motor because it’s easy to control and smoother/quieter than a stepper or servo. It should also be electrically quieter.

And of course, you don’t really need a microcontroller and software with a DC motor. :wink: I guess it depends if you are better at programming or if you’re better at making a simple logic circuit.

DVDdoug:
DC motor because it's easy to control and smoother/quieter than a stepper or servo.

I think if it was mine I would like it to go BZZZZZZZZ CLICK when it lifts the arm :slight_smile:

...R

Railroader:
Can You renovate the old Safety Raiser? What is wrong with it? What makes it unreliable? Is it the mechanical or the electrical part making it unreliable? Can that be repaired?

The Safety Raiser is purely Mechanical. The way it works is there is a spring loaded and damped piston in the base. The piston has a small groove cut just above the base when the spring is compressed. There is a thin wire that rides in the groove and holds the piston down. The wire is made of steel and is freely pivoted at one end. The wire is held in the groove by a small magnet very close to the piston. Then the wire is bent vertical and a small plastic ball is molded on the end just to improve visibility. When the tone arm touches the vertical section of the wire. the wire breaks free from the magnet and comes out if the groove. This releases the piston. The piston has a shoe on the upper end that lifts the tone arm.

It’s a pretty ingenous design. I have cleaned it and lubricated the mechanism & it is working OK now. The problem it was having is the tone arm would bump against the wire and skate back across the record. The side force from the tone arm was not enough to release the wire from the magnet. Cleaning and oiling did the trick.

Problems with the design are:

1 It’s easy to forget to reset the piston when starting the next side.
2 Also it’s easy to bump the wire out of position. When out of position the piston does not remain compressed.
3 Some side force on the tone arm is required to release the mechanism. I think this must be hard on the cartridge and record.

For these reasons I would still like to pursue an electronic solution. With optical or prox sensors there would be no contact with the tone arm.

Just electronics will not help You. You need to solve the mechanical part of the proj. Then You can advance.

Robin2:
It seems to me that using a small servo would be simpler. It has all the electronics inside.

Have you measured how much force is needed to raise the arm? The lifting lever is probably very close to the hinge point so the force may be greater than you expect.

With a stepper motor you will also need some sort of stepper motor driver. There is also the question of whether the stepper motor in your link can be run against its physical end-stops without damage. If not you will need some limit switches to detect when the slider is at the extremes of motion.

You have not said whether you have the equipment needed to detect when the tone-arm is at the end or start position.

An interesting project.

...R

The force is very small. Less than 3 grams at the stylus. Overcoming the inertia of the tone arm may be the greater force. I looked at servos and I think a Auto Headlight servo should work. Thanks!

Jagman:
The force is very small. Less than 3 grams at the stylus.

But I doubt if your apparatus will be lifting it at the stylus end.

I looked at servos and I think a Auto Headlight servo should work. Thanks!

I suspect that would be expensive compared to the hobby servos used for model airplanes etc. Also check if the headlight servo need a special controller.

...R

Robin2:
But I doubt if your apparatus will be lifting it at the stylus end.
I suspect that would be expensive compared to the hobby servos used for model airplanes etc. Also check if the headlight servo need a special controller.

...R

The headlight servo costs about $6.00 shipped. It has the electronics inside. it can be controlled by 2 1k resistors and a 10k pot. the travel is about 6-mm.

Jagman:
The headlight servo costs about $6.00 shipped. It has the electronics inside. it can be controlled by 2 1k resistors and a 10k pot. the travel is about 6-mm.

That's a lot cheaper than I expected. But, out of curiosity, why do you prefer that over a regular hobby servo which does not need any external components and works with the regular Arduino Servo library?

Also, what is the role of the potentiometer in controlling the headlight servo? If you want to mimic the potentiometer with an Arduino you will need a suitable digital potentiometer.

...R

PS ... you could go for the Heath Robinson / Rube Goldberg solution by using an Arduino to control a servo to rotate a regular potentiometer :slight_smile:

I have found a good and inexpensive solution for the tonearm lift. I picked up a parts unit Philips GA-312 turntable for free. The GA-312 has a well designed tone arm lift built into it. The lift post is spring loaded and damped with a dash pot. The normal position is up. To lower the lift post there is a rocker button mechanism that is connected to the lift mechanism by a flexable pull cable & cable housing. When you rock the button forward the cable pulls down the lift post. There is a vane on the bottom of the tonearm pivot that interrupts an LED that is shining on a light sensitive transistor switch. When the tone arm reaches the end of the LP the vane blocks the light from the LED. This closes a circuit and a solenoid fires and releases the cable tension & resets the rocker button. This allows the lift post to rise and lift the tone arm.

My SME tone arm cannot be fitted with a vane below deck to interrupt the LED light. Therefore, I have opted to close the solenoid circuit using a normally open reed switch. This can be closed by a small magnet attached to the tone arm. At the end of the LP the magnet on the tone arm approaches the reed switch and closes it. The solenoid fires and the lift bar rises.

I have bread boarded the circuit and it seems to work fine. I don't have any tiny magnets on hand so I orders some from Home Depot. When I get them I will let you all know how this works out.