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Old 15th October 2016, 02:41 PM   #1
Pyramid is offline Pyramid  United States
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Default DIY 4 Phase Sinewave Generator for Turntable Motor Drive

This is a shared DIY project for non-commercial use.

The SG4 generates 4 low distortion, high accuracy sinewaves suitable for driving conventional audio power amps to create a multi-phase drive for turntable motors. The generator outputs a reference sinewave at 60/81Hz or 50/67.5Hz on the 0 pin. The 90 pin outputs an exact replica of the reference sinewave, but shifted +90 (Cosine) for driving 2 phase AC synchronous motors. The 120 & 240 pins output an exact replica of the reference signal, but shifted +120 and +240 respectively for driving a 3 phase motor. The SG4 is a sinewave generator only. You will need to add the necessary audio Power Amps and step-up transformers (if needed) to create the final signal to drive the motor. Low cost linear and class D amps are readily available on e-Bay and other on-line sources. Working with High Voltage can be dangerous. Do not attempt this part of the project if you are not trained in handling power electronics: Seek competent technical help if needed.

The PCB uses all thru-hole components for easy assembly, but some soldering skills are still required. The P is a PLCC package but there is a socket for it on the board.

The project consists of a bare PCB, a parts "kit" available as a shared cart from Mouser electronics, a P with the operating system pre-programmed into it and the on-line documentation you see here.

The PCB is available from OshPark PCB fabricators at the following link: https://www.oshpark.com/shared_projects/KoCV8BH4
The PCB is created in multiples of 3 for a cost of ~$45 or $15/board.

The parts kit can be ordered from Mouser Electronics: http://www.mouser.com/tools/projectcartsharing.aspx
Enter the Access ID code: 6A27796F55. The parts kit to build 1 PCB costs $32.34.

The pre-programmed P is available in the US from DIYAudio member twystd via direct e-mail: twystd3atyahoo.com. Cost will be ~$7 and change plus shipping.

The pre-programmed P is available in the EU from DIYAudio member ralphfcooke via PM. Because of higher shipping costs to the UK, user cost will be ~10 plus shipping.

The following documentation is available below to aid in construction of the project:

SG4 Schematic.pdf
SG4 Parts Locator.pdf
SG4 Assembly Instructions.pdf
SG4 BOM.pdf (Generic bill of materials with part references)
SG4 CART.pdf (Mouser cart with mfr's part numbers and costs)
SG4.zip (Gerber X274 files if you want to use your own PCB fabricator)
SG4.png (X-Ray view of the PCB w/traces, pads and silk screen)

The SG4 uses a 20 bit DDS core implemented in software to generate the reference sinewave. Frequency resolution is 0.01Hz. Frequency range is 40.00-70.00 Hz for 33 RPM and 60.00-90.00 Hz for 45 RPM. There is an on-line video showing the frequency operation Here and a video for phase adjustment Here.

There are four 8 bit phase accumulators to generate the four phases. The reference signal is fixed, but the other 3 are adjustable in 1.5 steps 15 maximum. D to A conversion for the 4 signals is done with 8 bit PWM at 18kHz. There are 4 LPFs on the board to convert the PWM signal to analog. The outputs are DC coupled, 5VPP and centered at 2.5VDC. Distortion is ~0.5% (-46dB) and frequency stability is 30 PPM.

Update: The firmware has been updated to version 1.02. A 7 bit linear taper attenuator has been added to ramp the voltage from 0 to 5VPP at start up when exiting standby mode. This should prevent the amplifiers from shutting down when first started as they will have time (~650mS) to overcome the core magnetization of the transformers. I also added a reduced output voltage mode, where the output voltage will automatically be reduced to a user programmed level after 5 seconds. The level is adjustable from 128 (maximum) to 64 (half voltage) in ~40mV steps which equates to ~1V steps at the transformer outputs.

19-Nov-16: I returned the phase adjustment to 1.5/step. One of the peculiarities of using a 16 bit phase accumulator with an 8 bit DAC (PWM in this case), is the limited precision math can create different points where a carry occurs (and thus an additional phase step). For most frequencies, this isn't noticeable as the difference in phase shifts is usually in the mSec range. In certain cases, the math works out where it becomes quite noticeable and in the audio range where it could affect performance. Using a 16 bit phase accumulator in the SG4, a nasty phase spur will occur on either side of 81.92Hz, which is fairly close to the frequency needed for 45 RPM. The new firmware hasn't hit the field as of yet, so there will be no need to do another exchange. V1.02 will ship with the attenuator capability, but will retain the 1.5 phase adjustment of the original.

Users who upgrade to the new firmware should perform a Factory Default Reset after installing the new firmware.


28-Dec-2016: Just added the PCB files to OshPark for a Rotary Encoder to SG4 interface PCB. The circuit converts the 2 quadrature signals from the encoder to a single pulse train on the UP pin when turned CW and a single pulse train on the DN pin when turned CCW. The momentary push button switch of the encoder is connected to the STBY button of the SG4. This allows all of the normal operating functions to be performed by one rotary control.

The 1 inch square board uses all surface mount components in order to keep the size down. The IC is a CD4013 in SO14 package. C1 and C2 are both 0.47uFd Tantalum caps 10V rating in a 1206 size package. R1, R2 and R3 are not necessary if you use the Arduino Rotary Encoder which has the pull up resistors already on its PCB. If you use another encoder without pull ups, add the 3 resistors (all 10K 0805 size). Vcc is connected to the 5VDC output of the regulator on the SG4.

You can order the PCB here ($5 for three):

https://www.oshpark.com/shared_projects/AbsVI39H

The Encoder PCB can also be ordered with thru-hole component layout instead of SMT:

https://www.oshpark.com/shared_projects/W6QWOCOF


A suitable audio power amp and step up transformers are available here: 60-wpc-amplifier-diy-turntable-motor-drive
Attached Images
File Type: png SG4 PCB.png (52.2 KB, 1687 views)
Attached Files
File Type: pdf SG4 Schematic.pdf (60.2 KB, 581 views)
File Type: pdf SG4 Parts Locator.pdf (58.0 KB, 190 views)
File Type: pdf SG4 BOM.pdf (46.1 KB, 197 views)
File Type: pdf SG4 CART.pdf (50.8 KB, 180 views)
File Type: zip SG4.zip (98.4 KB, 151 views)
File Type: pdf SG4 Assembly Instructions.pdf (761.0 KB, 195 views)

Last edited by Pyramid; 28th February 2017 at 06:56 PM.
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Old 15th October 2016, 03:03 PM   #2
2wice is offline 2wice  South Africa
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Nicely done!
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Old 15th October 2016, 05:01 PM   #3
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All parts ordered or requested
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Old 15th October 2016, 06:50 PM   #4
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Pyramid,

My deep respect, you did an amazing job.
Ralph, you can count me in for a PCB + Processor.

Hans
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Old 16th October 2016, 01:58 AM   #5
jrubins is offline jrubins  United States
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Subscribed! What's the deal with the uP? Is there stock of the programmed up? What's the cost likely to be?


Sent from my iPhone using Tapatalk
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Old 16th October 2016, 05:45 PM   #6
Pyramid is offline Pyramid  United States
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Thanks for the kind words. Hopefully the results live up to your expectations.

jrubins- DIY member bfg4wd will be stocking and distributing the pre-programmed chips. Still working on the details...will update as soon as it is all sorted.
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Old 16th October 2016, 05:47 PM   #7
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Default I am in....

Hi,

Count with me for PCB, programmed PIC and if possible a full parts kit.

Congratulations to Pyramid, I appreciate your efforts with the DIY community.

Jorge
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Old 17th October 2016, 10:15 AM   #8
kffern is offline kffern  Australia
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Thanks Pyramid, that must have been a lot of work.

I'm in for at least one PCB + parts. Anyone else in Aus. interested? I'm in WA.

Dumb question #1: How would you box it to get the display visible? Wouldn't U1 touch the case? I guess you could mount the LCD and buttons externally with a ribbon cable?

Regards,
Kffern
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Old 17th October 2016, 11:10 AM   #9
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Many thanks Pyramid,

I'm interested
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Old 17th October 2016, 11:16 AM   #10
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Quote:
Originally Posted by kffern View Post
......
Dumb question #1: How would you box it to get the display visible? Wouldn't U1 touch the case? I guess you could mount the LCD and buttons externally with a ribbon cable?

Regards,
Kffern
Not a dumb question at all, the easiest way would simply be to add a socket for the display, and maybe either use pb switches with longer shafts, or, as you say, mount the pb switches remotely.

Last edited by ralphfcooke; 17th October 2016 at 11:17 AM. Reason: punctuation :(
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