Load cell morse code paddle

This is a concept of using load cell as Morse Code paddle Advantages :

• easy mechanical apply
• no moving parts
• fast and quiet
• cheap - Trinket + laod cells + AD ~25$
• auto calibration - no readjustment needed

In TrinketShielPaddle folde You can find KiCAD files + production files ready to send to *PCB make comapny

Some challenges during during construction :

Assumpion - max speed 100 WPM

Sume usefull link about timing: https://morsecode.world/international/timing.html

100WPM - 1dot = 12ms

AD requirements : Refering to Nyquist–Shannon law https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem sampling rate should be at least 167 SPS

Load cell gives differential voltage: ~0-1.5mV

ADS1115 - 16bit(12bit ADS1015), 860SPS, lowest range 256mV, Comparator, differential mesurement

• 860SPS - OK
• 16bit - OK - 0.0039mV/bit (ADS1015 - 0.0625mV/bit - too small resolution vs 0-1.5mV range)
• 256mV - bit too low (do You know some AD with gain >16 and built in comparator - then smaller resolution is requiered)
• Comparator - as a requierement ! - comparator output drives executive transistor directly
• Differential mesurement - requre for 4 wire load cell

Battery alert

• battery should never drop below 3.0V
• there is ~0.3V drop on diode+regulator (ATTINY85 should work properly till 2.7)
• Vcc measure using internal 1.1 reference
• 3.1 - drop = 2.8 = alert
• 3.0 - drop = alert + lock paddle

TODO :

• AD1115_wa lib cleaning
• other A/D ?
• i2c connection autodiagnose work on Arduino Nano but not on Trinket
• Fully printed housing + paddles will be nice addon (OpenSCAD)
• E/V/HST test - passed HST by SP7VV
• issue with charging circuit
• after some time of use in setup mode paddle start working in reverse mode, need to be pulled instead of pushed - partially done: -poor chineese load cell change their "zero" point in time, also beacuse of that new approach with autocalibration is done -setup part should done with same approach as well TBD