step-up/README: detailed description of the project

diff --git a/projects/step-up/README b/projects/step-up/README
index a7a2a8672080f934bbec798711f506e8b4163455..2d4c661f5fc51183c925f171a95f01bce1bbf546 100644 (file)
--- a/projects/step-up/README
+++ b/projects/step-up/README
@@ -1,9 +1,29 @@
-Step-up converter with current feedback measurement.
+Simple bike lights:
+
+Step-up converter with current feedback measurement
+Battery voltage monitor
+Status LED
+Button
 
 CPU: ATtiny45
-Driven by PWM output OC1B (PB4 pin) with MOSFET.
-Current feedback measured at ADC3 (PB3 pin).
-Output on the PB4 header (pin 1 is negative, pin 2 is positive side).
+
+Step-up converter:
+       Driven by PWM output OC1B (PB4 pin) with MOSFET.
+       Current feedback measured at ADC3 (PB3 pin).
+       Output on the PB4 header (pin 1 is negative, pin 2 is positive side).
+Battery voltage monitor:
+       Uses ADC1 (PB2 pin), voltage is divided using 1M5 and 100K resistors,
+               low-pass filter added on input (R30 capacitor, R32 resistor)
+Status LED:
+       Uses PB1 pin, R22 resistor, positive side is PB1 header pin 2,
+               negative side is PB1 header pin 1
+Button:
+       Connected to PB0 header pin 2 using R12 0-Ohm link R12,
+       negative side is PB1 pin 1 (alternatively PB0 pin 1 could be
+       used instead - 0-Ohm link R15 needs to be added). Internal
+       pull-up resistor of ATtiny itself provides the voltage.
+       Pins 2 and 3 of PB2 header are shorted, and 100K resistor R3x
+       is added between pins 1 and 2.
 
 
 Bill of materials:
@@ -14,18 +34,89 @@ D50 SS24 Schottky diode (SMB package, 40V, 2A)
 L50    470uH, 390mA, 200 mil pin distance (probably too big for 20mA LEDs :-)
 PB4    two-pin header soldered to pins 1 and 2 of PB4
 Q50    IRLML6344TRPBF N-channel MOSFET, 30V, 5A, SOT-23 package
-R40    220nF capacitor (not resistor!)
+R30,R40        220nF capacitor (not resistor!)
+R32    15K
+R33    1M5
+R3x    100K (see above)
 R45    1K5
 R50    15K
-R51,R53        0R00 (zero-ohm link)
+R12,R51,R53    0R00 (zero-ohm link)
 R55    3R0 (can safely measure currents from ~1 mA up, for higher currents use lower value)
 U1     ATtiny45-20SU
 U2     MCP1703T-5V
 
 
+Pin-out:
+
+PB0 header:
+       2: button +
+PB1 header:
+       2: status LED +
+       1: status LED -, button -
+PB4 header:
+       2: LED string +
+       1: LED string -
+
 Firmware:
 
 The firmware is a dumbed-down version of firmware for my other
 project: http://www.fi.muni.cz/~kas/bike-lights/, modified
 for ATtiny45.
 
+
+Theory of operation:
+
+After power-up, the firmware sets up the CPU and powers it down,
+waiting for a long button press. In this condition the system
+takes about 8uA from the 9V battery. So a typical 500 mAh 9V battery
+would last about 2604 days in this mode.
+
+When the button is pressed for a sufficiently long time, the CPU
+wakes up, switches the status LED on (providing visual feedback),
+and starts blinking.
+
+The firmware main loop is timed by ADC interrupt. It continuously measures
+the voltage on R55 feedback resistor, and adjusts the PWM value on OC1B
+to match the expected current through the LED string. Occasionally
+the ADC is switched to the battery voltage sensing, and the battery
+voltage is read. If the battery is critically low, the system
+is switched to the power-saving light pattern (see below).
+
+The step-up converter has four target values of current (2 mA,
+6 mA, 12 mA, and 20 mA as of this writing, see pwmled.c). The blinking pattern
+is adjusted separately from the target value in the firmware.
+
+The firmware recognizes short and long button presses. The short one
+cycles through all blinking modes, the long one switches the system off and on.
+
+The status LED has two blinking modes:
+- in the normal one, it is off by default, and uses a series of
+       short switch-on blinks to display the battery voltage
+       (the number of blinks is voltage above 7V in 0.5V steps).
+- when an error occurs, the status LED stays on by default, and displays
+       the error condition as a series of short switch-off blinks:
+       - one blink is a "power low" condition
+       - three blinks is "step-up error" (a LED string disconnected,
+               for example).
+- when the long (-enough) button press is detected, i.e. when powering on
+       or off, the LED is switched on to provide a visual feedback
+       of long-enough button press.
+
+The blinking modes and patterns are currently set up as follows:
+1. power-saving minimal mode
+       - a single short blink at minimum current
+2. blinking mode 1
+       - 2 and 3 blinks at the second-lowest current
+3. blinking mode 2
+       - 2 and 3 blinks at the third-lowest current
+4. blinking mode 3
+       - 2 and 3 blinks at the highest current
+5. steady light at the minimum current
+6. steady light at the second-lowest current
+7. steady light at the third-lowest current
+8. steady light at the highest current
+
+The system starts up set to mode 3, and switches to mode 1 when
+the power is critically low. Other modes can be chosen via short
+button press.
+