How to check whether a turntable is playing / rotating

Hardware
#1

Hello,

Question
Which sensor is suitable for detecting whether a turntable is rotating or not? Can this be achieved by a motion sensor or vibration sensor? Which microprocessor would be a good choice to make a battery powered system, which could be placed above my turntable or attached to the dusk protection.

Background
I have an automation which is switching off my HiFi, if no music is playing for some time. The HiFi is quite good, but pretty old, so I connected a Bluetooth Dongle to play music remote from our phones. I am using a smart plug as switch and have an automation which reads our phone sensors to check whether a phone is connected via Bluetooth and if it is currently playing music. So far so good - everything working fine, but now I have a problem where I hope to get an advice:

I am also playing music via a turntable connected to the HiFi now and then. I tried to prevent automatic switching it off when the music is playing via turntable by checking if the power reading from the plug exceeds a certain value (once the turntable is rotating the motor needs some power and my smart plug measures about 1 or 2 W increase in power). My problem is that this is a very inaccurate way to determine if the turntable is playing or not, which is only working if the volume is at a certain level.

Idea
I want to use a sensor connected to something like ESP8266 or 88w8801 to check if the turntable is rotating. The system must be small and battery driven. Unfortunately I do not know a chip that could do this even better using ZigBee - does someone know if a ZigBee ic exists?

#2

Why does the device have to be battery driven? I presume that the turntable runs off the mains, anyway.

For detecting whether the turntable is running I can suggest two venues:
One: if the turntable motor is connected to the power supply. Couldn’t you just attach a device that sends a signal (any signal at all) while it is connected to the power supply and connect it to the same supply as the turntables motor?
Two: if the turntable has a stroboscobe rim around the platter, could you devise a gadget which detects the stroboscope moving past an optical cell?

1 Like
#3

First of all: Thank you a lot for your 2 ideas. Both of them are very helpful and I need some time to evaluate which one I will use!

My initial idea was to make a gadget like your second idea, which could be simply removed from the turntable if not needed anymore. The usage of batteries was personal preferability, because I do not want to have additional cables around my HiFi.

I thought about idea 1). before, but it always looked as the more “dangerous” option to me. I would need to solder inside my turntable, which I would prefer not to do. I thought I would need to attach a cable to a suitable position inside my turntable and connect it to an GPIO of my microcontroller (prob need a limiting resistor and common grounds with the turntable as well). I am not able to predict if this change of the schematic could have any sideeffects to the components of the turntable.
But after your input I see that there are big advantages to this solution… I could use the turntables power supply and would not even need an additional sensor. I do not even need a GPIO connection, because the microcontroller would only be powered if the turntable is powered anyways. So sending e.g. a ping over WiFi could be enough for my automation. I am going to open my turntable to see if there is enough space to place something like a sparkfun ESP8266 inside.

Option 2) is also possible in my case and I did not think about using the stroboscope, yet… This means I could just use a LED as optical sensor and poll the ADC to detect if it changes (transition of black and white squares)…

1 Like
#4

Does the TT have a dedicated ON button or is it a speed selecting knob? If the latter, just use a double relay to delect each speed. Since the relay is stateful, you will know if it is on, and at what speed.

If it’s an AT LP120 or other Technics styled TT then you will lose speed knowledge in your automation, but but could still relay the push button.

ETA: Most TT wall warts are 9v or 12v dc (or there’s a dc conversion inside). Here’s a relay that can work using the TT’s own wall wart if technics style (they also make a double relay so you could do the speeds)
https://www.amazon.com/MHCOZY-Adjustable-Selflock-Momentary-SmartThings/dp/B08X218VMR/

Just re-wire your push button or speed select knob to the GPIOs and that way you preserve physical control in addition to stateful play status. Heck, you could even set it to deactivate after 20 minutes and save the dead wax portion of your records / your needle life.

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#5

It is actually a Technics SL-DD 33, so its an automatic TT, which has a physical start button. This sounds like a great solution, because I would also be able to remotely start the TT, which I was not aware that it might be possible that easy.

I was already looking at the schematics and found that unfortunately there is no 3.3V or 5V potential to connect an ESP, but indeed there is a step down to 12V, which would fit the module you linked. Only downside is that it is a bit pricier and consumes somewhat more power compared to the ESP. It also is quite a bit larger and I hope that it fits inside the TT, which is rather small.

With GPIOs you do mean the pins from the relay, right?

I just ordered one, but probably am going to end up using a lot more of these handy ZigBee relais :). Thanks! That was exactly what I was looking for…

#6

AH! My head is stuck in esp-land because I have been doing a project. By “GPIO” I meant just wiret the technics button to the pads of the manual engage button / pairing button on the relay board. Since the technics button is momentary it should be a decent match.

Actually, having an auto it could even be simpler. Momentary ‘play’ button press just sets a timer for 23 minutes (one side of an LP + some extra time just to be safe). Each press of the button resets that ~23 minute timer. So your off automation could be like:

  • If timer == 0
  • if connected bt devices == 0
  • turn off amplifiers and equipment

or something equally easy. One nice thing about the relay is being a non-battery device it will reinforce your zigbee mesh. But also being an auto table, you might be able to go even easier. I think somebody was hacking amazon dash buttons for a while. …

#7

I don’t worry a lot about the automation part. I will probably use a timer, because I already use one for my current automation checking every 30 minutes whether music is still playing. Good thing about a timer is that automation will even work if HA is restarted.

I can just see two very little issues with this automation, which are totally acceptable for me:

  1. you only play half of the LP and switch it off → the timer gets reset and the automation wont turn it off for another 30 minutes
  2. you start playing the LP at a different position than the first track to skip a few songs (same as 1 - automation just will shut it down a bit later)

I do not own an Amazon Dash button so I think this option is not better for me than using that ZigBee relay or an ESP… I would also lose the benefit from the relay of controlling it remotely using such a button, no?

#8

I do believe the dash button would lose you some functionality.

I wanted to look at the TT schematics before comment too much more, but I think this is a modification which would work. The TT has 18VAC internally which the relay can operate on.

The schematic makes the start switch look stateful so I’m not 100% sure how the module would react to the button being held? But if you just feel a momentary press then that’s great.

Basically the ‘inching’ (timed) relay could be set to emulate a single tap or a ‘latch’ and all the power is there internally.

The timer was just an idea for a simpler modification if you were planning to cut power from the wall for the turntable.

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1 Like
#9

Sorry I did not have the time to answer and thank you for the schematics yet! So, thanks a lot for your efforts to help me :).

My module is looking slightly different (the ‘manual switch’ button is rotated by 90 degrees), but it shouldn’t be too much of a problem. There is only less space for soldering, but it should stay the same otherwise… I guess I have to measure which of the connections from the button are shorted, anyways…

The button seems to be momentary, so there should not be a problem starting rf pairing mode by holding the TT start button, but I will try it out :smiley:

I hope that I can try it out within the next days. I will let you know if everything worked out!