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Hard Disk Drive analog and digital clock

How to build a fully working noiseless HDD clock. Almost a piece of art !

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This is a quite old project that I made 9 years ago. As it has still quite a lot of success with my friends, I will perhaps take the opportunity of this hackaday's challenge to update it with a more modern MCU.

You know what I mean ? "Hack it Back" : Your project adds new capabilities to older electrical gear to keep it useful.

Old Hard Disk Drive are totally useless... until you open them and discover that they are incredibly "nice"... well for geeks as we are !

Why not building an original smart clock "analog and digital" literally speaking !

A long time ago I made a first HDD clock. This video became very fast "viral" not because of the clock itself but because of the noise this clock made... (Today almost 500k views !)

It was a lot of fun but really this clock was totally unusable...

Here it is, you can laugh if you crank up the volume !


I could have stopped here my investigations with Hard Disks Drives but I wanted something quieter (even noiseless) and which could stay in my home without being immediately destroyed by my wife... So something "almost pretty".

The result is this analog + digital clock that I made from another hard disk

My first attempt was this one :

All the inner parts of the drive look like untouched, the arm is fully moving and displays the minutes  for each hour. The disk is rotating just every "full" hours.

The motion is smooth and somewhat adictive.

Here is the first video of the clock : we were ten years ago and it was 10:30 am

Now let's see how all this works and how you can do your own "HDD clock".

This project was published on my Website ten years ago, but I will now publish the whole design, the source code, everything in open source and open hardware.

And, If I am not too lazy, I will as well try to port it on an ESP32 MCU and design an android App to get rid of the PC App which is a bit outdated today!


choosing the right disk

Let's start by choosing the right disk model. Almost any HDD will work but one important thing is mandatory : you must have at least two platters into the disk. We will see why later !

A Hard disk drive is, by itself, a nice "piece of art". It's a precise mechanism with a shining almost perfect mirror.

I decided to keep as much as possible of the original HDD to convert it into a working clock.

My specifications were as follows :

  • as little visible modifications on the disk
  • the head arm should indicate the minutes
  • the rotating disk should indicate the hours
  • the device should be automatic on startup
  • the disk should be powered by any 5V coming either from a USB charger or directly from a PC USB host
  • a USB interface should provide access to a software to tune and setup the device (plug & play)
  • Time should be kept in case of a power failure
  • clock should be noiseless


Modifying the heads arm

Wikipedia tells us that a moving-coil galvanometer is a type of ammeter: an instrument for detecting and measuring electric current. It is an analog electromechanical transducer that produces a rotary deflection of some type of pointer in response to electric current flowing through its coil in a magnetic field.

The D'Arsonval/Weston galvanometer used today is constructed with a small pivoting coil of wire in the field of a permanent magnet. The coil is attached to a thin pointer that traverses a calibrated scale. A tiny torsion spring pulls the coil and pointer to the zero position. When a direct current (DC) flows through the coil, the coil generates a magnetic field. This field acts against the permanent magnet. The coil twists, pushing against the spring, and moves the pointer. The hand points at a scale indicating the electric current

Our HDD heads arm is almost a galvanometer but it must be equiped with a litlle torsion spring to convert it into a DIY moving-coil galvanometer

When I said that this clock would be "analog and digital" I wasn't lying at all... this galvanometer is fully analog. And we will see that the rest of the clock is much more digital!


Adding a position sensor

When the disk rotates you don't know what is its position. As we will engrave the platter with hours marks, we need to have a way to know "where is noon".

A RPR220 phototransistor is soldered on the PCB (details will come) and its led focusses IR beam on the bottom platter of the disk. A hole is drilled in the disk enclosure for that. A dark spot is painted on the disk to be detected easily by the sensor.

On the left side picture you can see half...

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USB Device - HID - JP_HDD_Driver.hex

PIC firmware .hex file

hex - 65.90 kB - 07/09/2022 at 08:25

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JP_HDD_Still_Clock_eagles_files.zip

The whole eagle files packages (schematics + PCB)

Zip Archive - 419.93 kB - 07/08/2022 at 13:33

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clock.TAP

platter engraving GCODE

tap - 314.63 kB - 07/08/2022 at 10:45

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CLOCK_ARMS.DXF

template of the clock to be carved on the disk platter

AutoCAD DXF - 215.27 kB - 07/08/2022 at 10:41

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  • ESP32 HDD clock schematics

    JP Gleyzes07/31/2022 at 08:56 0 comments

    As promized, I am just starting to port my HDD clock on a new MCU : ESP32

    This would have several adavantages:

    • wifi and bluetooth are enabled. No need to connect to a PC via USB
    • ESP32 lolin lite breadboard has everything needed: power supply, battery, USB to serial programmer
    • no need for the RTC chip as wifi connection is available to get time over NTP
    • easy to hook up an android App to this MCU 

    Here are the simplified schematics

    It's indeed much simpler than the PIC circuitery !

    • one mosfet is still needed to drive the coil  
    • one L6234 to drive the BLDC motor.
    • one RPR220 as a position sensor.

    stay tuned for the PCB and the code (will take a few weeks...)

  • Calibration of the heads arm coil

    JP Gleyzes07/09/2022 at 08:43 0 comments

    The heads arm coil bhaves as a galvanometer.

    However its behavior is not totally linear. Thus the minutes ticks could be a little unprecise...

    A calibration procedure is needed!

    I have choosen to calibrate the minutes every 5min. It meens that a multi linear curve is applied to fine tune the PWM value applied to the coil.

    Once again you can use the PC application to interactively enter these calibration values. You will have to enter 5 values (00:00, 00/15, 00:30, 00:45, 01:00)

    • check the box  
    • you can now move the horizontal scroll bar 
    • positon the arm to 00:00; 00:15 ; 00:30 ; 00:45 ; 01:00 and each time write the value in the adhoc text box (example for 00:30)
    • save these values in eeprom 

    Your coil arm is now calibrated!

  • Alignment of the photransistor sensor

    JP Gleyzes07/09/2022 at 08:32 0 comments

    You need to align the phototransistor pulse on the 6th stable position of the motor and also align the clock platter to the 12h00 position.

    The PC application is here to help you!

    • tick the checkbox  
    • the disk will lock on the calibration position.
    • unscrew the platter
    • rotate the bottom disk until the led switches on
    • rotate the top platter until it shows "12:00"
    • screw again the platter fixations

    As it is not totally easy to understand, have a look  at this video 

    Your disk is now ready to run. Anytime the led flases, a full rotation is finished!

  • Driving HDD BLDC motor

    JP Gleyzes07/09/2022 at 08:06 0 comments

    A Hard disk drive motor has more coils than this simple triphased motor. Practically I have found 24 stable positions. 

    The basis sequence of 6 positions is thus repeated 4 times. And 24 is a very convenient number for a clock !

    As we have 24 stable positions, we can have twice 12 hours marks very easily. Simply power the coils on the stable positions in sequence and the disk will jump as would do a stepper motor on these positions.

    This being said we still need a way to trigger the coils depending on the current position of the rotor...

    The simplest method to drive a BLDC is to have a motor equiped with hall sensors. These three sensors are positionned just in between the stator teeths and allow to trigger 3 successive stable positions of the rotor. (On the picture you can see an old floppy motor with its Hall sensors clearly visible). Note the positions of these sensors which are the same as the stable rotor positions on the above picture.

    A hard drive motor does not have hall effect sensors... They use another technics to find the rotor position. This "sensorless BEFM" technics is efficient but much more complex to implement...

    I have thus decided to replace the hall effect sensors by a single sensor : the RPR220 phototransistor.

    This sensor allows me to check the 12:00 position of the clock and to check the stable position 6 of the rotor. The bottom platter must be carefully aligned with this stable position. I will show you latter how to do. 

    This being done, knowing that there are 24 stable positions, you just have to know the duration of a full rotation, to divide it by 24 to get the duration of a full step. You can commutate the position n°1 when you see the dark spot and then trigger the following 23 steps in sequence.

    Basically it means that instead of having 3 hall sensors we only have one.... Thus if you want to rotate the disk you just have to "launch the rotation" using the stepper mode technics (increment the driving sequence one by one). when you see the phototransitor pulse you are on position 6. 

    Now go on pulsing the sequence but at higher speed and measure the time to see again the RPR pulse. Knowing this rotation period you can estimate the theoritical timing of the two missing sensors and trigger the respective pulses precisely. And increase the speed...

    This is exactly what is implemented into the firmware. Simple and efficient unless you want to increase too much the speed... where the motor will stall!

    It may seem simple but bear in mind that you have to start the disk in "stepper mode" accelerate it and when the speed is high enough switch to brushless mode. It can be a little tricky mainly if you remember that the disk is a 12V one powered only with 5V...

    Of course the coils are not directly powered with 5V DC but are powered via a PWM signal to limit the current into them and to tune the rotation speed.

  • Electronics schematics

    JP Gleyzes07/08/2022 at 13:29 0 comments

    Electronics is based on Microchip PIC 24FJ256GB10. microcontroler. This 16 bits MCU has a native USB port which allows easy interface with a PC.

    It has also 9 hardware PWM ports which are perfect to drive motors.

    Together with the PIC we find :

    • A triple H bridge driver L6234 used to pilot the motor
    • a Reflective photosensor (photoreflector) RPR220
    • a real time clock calendar DS1337C used to keep time when the power is off
    • an audio amplifier MAX9716 for the clock to speak (to be done)
    • a 3,3V voltage regulator
    • a few SMD components to "make the glue" The schematics are quite simple :

    Note that you can safely forget the audio amplifier part which was only added there "for fun" (see the devoted log to be published)

    The motor is driven by the H bidge driver L6234

    Its outputs are connected directly to the motor connector scavaged from the original board.

    Note that VS pin is said to be 12V, but I do power this system only with the 5V DC coming from the USB plug.

    It works, the motor is not rotating very fast but it is enough for a clock and the H bridge does not heat at all !

    Furthermore, you do not need to add any external power supply, only a smartphone charger !

    The heads coil is driven directly via a PWM pin issued from the PIC. The Mosfet is there to cope with the 3.3V limitation of the PIC's IO...

    Finally the photo transistor is powered at 5V and is connected to a 5V tolerant input pin of the PIC :

    That's all for the schematics which is finally quite simple.

    You can find all the eagle files including PCB here.

  • Engraving the disk platter

    JP Gleyzes07/08/2022 at 10:35 0 comments

    You need now to design a nice "clock platter". 

    The disk geometry is directly influencing this design.
    You need to make a precise plan of the disk, axis positions, head arm lenght... and to report all this into a CAD software. here is my design for my old samsung disk.

    Here is the dxf file for this drawing


    A have tested several ways to transfer this drawing on the disk.:

    • toner transfer method with a laminator and a laser printer ( toner transfer). Result is clean but very fragile and there is a lack of accuracy when positionning the drawing on the platter. (see picture on top of the project page).
    • V shape engraving with my CNC mill. Result is almost perfect even though signs are a little too wide...Here is the GCode engraving file

    this video has been accelerated (High speed milling) 


  • Adding a phototransistor to the disk

    JP Gleyzes07/08/2022 at 08:58 0 comments

    RPR220 phototransistor is soldered on the PCB and its led focusses IR beam on the bottom platter of the disk. A hole is drilled in the disk enclosure for that. A dark spot is painted on the disk to be detected easily by the sensor.

    It is highly recommended to position the PCB on the disk before soldering the RPR220 sensor. Doing so will allow you to use the 4 pins holes to mark the disk enclosure and so to easily position the hole on the enclosure.

    Idealy the phototransistor should fly at 6mm of the dark mark. Fine tune the pins lenghts if necessary before soldering.

    However it is not that critical, a calibration procedure exists and will be described later. Provided that the phototransistor sees the dark mark, everything will be fine!

    Similarly the dark mark do not has to be recise at all. Paint it manually on the disk using a permament marker.

    You can remove the original PCB, but take care to unsolder the HHD motor ribbon connector. It will be reuse on our new PCB.

    Do not damage the motor ribbon!

  • Modifying the heads arm

    JP Gleyzes07/08/2022 at 08:17 0 comments

    Open your HDD and remove the heads arm :

    1. remove the upper half magnet
    2. unscrew the the platter locker screws
    3. unscrew the connector screw
    4. unscrew the screw on the central axis of the heads arm

    The magnet is very strong, it is uneasy to remove it. You can use a screwdriver to help you, but beware that the coil is very fragile... and is absolutely needed for this clock. Same thing for the connector and the ribbon!

    The heads arm must be equiped with a litlle torsion spring to convert it into a moving-coil galvanometer..

    The torsion spring is dissimulated under the heads arm. It is totally not visible.

    1. the heads arm is drilled and a piece of piano wire is epoxy glued in the hole
    2. the heads are properly removed and their fixations are slightly bended to avoid to touch the disk. .
    3. You need to find the two biggest wires on the connector. They shoud be the coil connections. We will use these connections to power the coil.

    Removing the heads can be a delicate operation. Take your time, do it cleanly at least for the upper head (the only which is visible and used a the "hour pointer". So my advice would be to finish by this one and learn on the bottom others !

  • choosing the right HDD

    JP Gleyzes07/08/2022 at 07:52 0 comments

    I had in my electronics garbage this old Samsung HDD

    You can still find similar products on ebay. (Google search for Samsung 1.08GB HDD)

    SAMSUNG WN310820A (1.08GB) with Firmware FH100 Information

    Common characteristics
    ManufacturerSamsung
    ModelSAMSUNG WN310820A (1.08GB)
    Capacity1 GB
    InterfacePATA
    Performances
    Maximum interface speed16,7 MB/s
    Maximum read speed2 MB/s
    Minimum average access time18.0 msec

    Their perfomances are not exactly impressive, but smart enough to build a clock !

    And they do have a lot of advantages:

    • internal bowels are "on top" the enclosure after removing the cover. They are totally visible which is nice!
    • they do have 2 disks platters which is mandatory
    • the heads arm is sharp and thus will make a perfect pointer
    • black color is very tendance and enhances the shining platters!

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Discussions

JP Gleyzes wrote 07/20/2022 at 20:51 point

Thanks.

Right but you don't know where is located the upper platter... So it will remain a manual process.

And the time is not stable

 as the speed may vary.

Finally this "calibration" is not that complicate!

(4 screws to tighten !).

  Are you sure? yes | no

Steve wrote 07/20/2022 at 18:45 point

Nice job.

A suggestion: instead of going through a laborious process to calibrate the ir position sensor, just put the mark "anywhere" and tell the pic, through the setup routine where the mark "is". It can then compute the offset to the current time.

The mark could be a radial line from the hub to the edge, simplifying the initial placement of the ir sensor.

Fun project. :-)

  Are you sure? yes | no

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