I recently recorded a tape and had to rewind and then to go back to the previous position. With the analog counter that was quite a challenge. Thus I thought by myself it would be great to set a marker and go back and forward to the desired positions. And to see minutes and seconds would be even better.
Well,just get a OLED display with I2C and since I kept the I2C bus on the Revision B of the CPU replacement I was able to connect it. No problem so far but all I/O pins are already used so I had to connect a switch for reseting the timer and to store a particular position to the LED output pin I used for debugging. It is easy to witch the output pin to an input and the LED the circuit does accept this. Everything is already designed in Revision D with SMD 1206 parts. Like to order the PCBs the following days.
Of course such a counter would only make sense if starting from the beginning of the tape with 0. When the tape reaches the end the counter gets automatically reseted. I also do not accept negative min & secs like the confusing displays on my old Denon Cassette Deck.
However, the real problem was to measure the correct time on fast forward or rewind since I cannot measure the mm the tape moved, only the elapsed time of the spinning tape. At the beginning, when the active tape wheel is almost empty the diameter and the length of the moved tape per rotation is less than at the end of the tape when the diameter of the active shell is higher as well as the length of the moved tape after one rotation. Complicated, but it seems it is working.
Although not perfect, since I use a 45 minute side for calculation and for a 30 minute per side tape the calculation would be a little bit different. Thus because I use the length in meters of a tape to measure the moved length of the tape.
To jump to a particular position is used the negative track numbers when programming the tape. instead at stopping at track 1 a click in previous jumps to the following options:
- C0 – jump to position 0
- P1 – jump to stored position 1
- P2 – jump to stored position 2
- P3 – jump to stored position 3
