Well, one idea to figure out the current tape position was to measure the current of the motors when playing the tape. There were several devices I had in history which I can remember that did it that way. I expect a difference in the current when the tape is at the very beginning and at the end of the tape. Maybe a little bit naive that it is working with the given hardware, but let’s see…
Therefore, to do some research I ordered a INA219 IC to measure the current. Since it can be connected via I2C bus it would be perfect and easily to implement on my board. In the meantime Unit #3 was already half reassembled and ready for this research.
After wiring the INA219 to the board and after I wrote the source code I pretty quick figured out the thing is very inaccurate. The measurement has to be very accurate but the values delivered from the INA219 were not exact enough. Moreover, the values for the capstan motor were almost the same as at the beginning or end of the tape. Ok, I am not a professional when it comes to tape decks – hell, not even used a tape for decades.
The next idea was to measure the current at the reel motor. Again no values measured which could help to figure out the current position. There is basically no difference measured by the INA219 and the values can only tell if there is a voltage or not but not in the detail that would be necessary.
Even tried to use a capacitor and other suggestions I found at the internet but none of them helped to get better results. Below you find some measures from the sensor during playback.
However, I failed with this idea and will stick to the current solution.
10:57:53.807 -> Bus Voltage: 2.12 V
10:57:53.841 -> Shunt Voltage: 5.77 mV
10:57:53.841 -> Load Voltage: 2.13 V
10:57:53.879 -> Current: 56.40 mA
10:57:53.917 -> Power: 122.00 mW
10:57:53.917 ->
10:57:55.918 -> Bus Voltage: 2.18 V
10:57:55.955 -> Shunt Voltage: 5.36 mV
10:57:55.955 -> Load Voltage: 2.19 V
10:57:55.993 -> Current: 53.70 mA
10:57:56.027 -> Power: 118.00 mW
10:57:56.062 ->
10:57:58.221 -> Bus Voltage: 2.20 V
10:57:58.221 -> Shunt Voltage: 5.69 mV
10:57:58.256 -> Load Voltage: 2.20 V
10:57:58.292 -> Current: 57.20 mA
10:57:58.330 -> Power: 122.00 mW
10:57:58.330 ->
10:58:00.345 -> Bus Voltage: 2.50 V
10:58:00.345 -> Shunt Voltage: 6.68 mV
10:58:00.378 -> Load Voltage: 2.51 V
10:58:00.417 -> Current: 66.70 mA
10:58:00.417 -> Power: 168.00 mW
10:58:00.453 ->
10:58:02.622 -> Bus Voltage: 2.52 V
10:58:02.657 -> Shunt Voltage: 6.66 mV
10:58:02.657 -> Load Voltage: 2.52 V
10:58:02.693 -> Current: 66.40 mA
10:58:02.693 -> Power: 168.00 mW
10:58:02.731 ->
10:58:04.738 -> Bus Voltage: 2.50 V
10:58:04.772 -> Shunt Voltage: 6.71 mV
10:58:04.772 -> Load Voltage: 2.50 V
10:58:04.809 -> Current: 67.50 mA
10:58:04.847 -> Power: 168.00 mW
10:58:04.847 ->
10:58:07.036 -> Bus Voltage: 2.40 V
10:58:07.036 -> Shunt Voltage: 7.52 mV
10:58:07.071 -> Load Voltage: 2.41 V
10:58:07.071 -> Current: 79.70 mA
10:58:07.105 -> Power: 184.00 mW