Hooking up TASCAM TT-M1 to STM32F4 Discovery board

I wrote about my working HID interface in the previous post. Now I can send data to my laptop in a convenient way in a simple HID report because I wrote a Delphi program to send and receive HID reports years ago.
Next step is to wire the Tascam TT-M1 scratch control unit to the board. As STM32F4 series have quadrature encoder interface in some timers, I can easily count the pulses without any line of code in my main loop or without using more interrupts or processor load.

IMG_0921 Continue reading

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Reverse engineering Tascam TT-M1 unit

Here is the simplified schematic of Tascam TT-M1. And the connecting part of the CD player, how it seems to work.

schemeit-project

There is a KE-204 optical encoder with a 360 tick encoder wheel. The 5V power is provided by the CD player for the unit. The push button generates a signal for the CD player to send the power I think.

Here are some pictures of the disassambled unit.

IMG_0872 IMG_0877 IMG_0879 IMG_0880

The Channel A and Channel B signals are 5V square wave signals. The phase shift should be 90 degrees according to the datasheet, but it seems to be incorrect.

tek00009 tek00010 tek00013 tek00017

Some crosstalk can be seen in the scope, but It is perhaps because of the measurement conditions, and the lack of chassis grounding.

The Tascam wheel turns 8-9 while the vinyl turns 1 rotation. It means that the base frequency is about 1660 Hz, but it is only an estimation. It is close to the time code vinyl base frequency fortunatelly, so similar range could be used for both applications. 0Hz – 4 KHz roughly.