drewsum
commented
3 years ago Using a cheaper parallel LCD module may get complicated since most of what I'm finding on aliexpress requires 5V VDD. This would require a level shifter and +5V power supply since the PIC32MZ and everything else must operate at +3.3V.
Finding a +3.3V VDD tolerant LCD module would be killer.
Potentially something like this: https://www.aliexpress.com/item/1005001537624067.html?spm=a2g0o.productlist.0.0.39b423f917jf19&algo_pvid=ef203fd2-e159-4604-b272-1e7de12f4989&algo_expid=ef203fd2-e159-4604-b272-1e7de12f4989-0&btsid=0bb0624316080712055828373e39af&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_
Remove as many unique components as possibleMake as many expensive features hardstrap configurable/BOM configurable as possibleChange input protection circuit to monolithic solutionLeave telemetry, just add a bunch of 0 ohm resistors across current sense resistors for PNP to handle (or replace with 0 ohms altogether)Add ferrite beads on POX sensor rails, lots of bulk bypassRemove excessive IC bypass - change from 0.1uF || 10nF || 1nF to just 0.1uF || 10uFConsider removing external oscillator - is the added clock inaccuracy acceptable? Or make this BOM configurable?Change display to a similar 20x4 character screen with same parallel interface, just find something way cheaperMake entire USB circuit BOM configurable, breakout UART to FTDI header to plug a dongle into deployable configAdd level shifter to USB UART, copy from Analog Clock (this worked well)change heartbeat to PWM rather than pin toggle, similar to analog clockChange all LVC1G parts to 74LVC1G97 for easier PNP placementMake TOF BOM configurableSee if you can make everything work off of +1.8V, so that the POX sensor and the MCU can share the same voltage railRemove LCD contrast potentiometer in favor of fixed resistorsRemove LDO from cap touch pushbutton, this is unnecessaryConsider battery, but for cost reasons, this will probably be a hard passFind cheaper hardware (screws, standoffs) from another source than digikey?Make all PGOOD LEDs powered from +3.3V_PGL like on Analog Clock, or use NAND gates to drive instead of inverterSwitch to 0603 passive components from 0402s? Talk with Nick CMake sure all PGOODs are routed to MCUUpdate to PIC KIT 4 programming header, or find more dense 8 pin solution and make breakout boardIf leaving +1.8V LDO, try to find a fixed output version, to avoid placing feedback resistors, same with +3.3V buckCheck in with Nick C to see if he thinks using a QFN MCU package would be better than TQFPAdd a sheet specifically for configuration hardstraps?Add all configuration hardstraps to "Misc Circuits" sheetConsider replacing specific resistor values with different parallel/series combinations of more simple valuesReplace all 499 ohm resistors with two parallel 1k resistors, or use a specific value used in a precision use case on the boardFigure out if we actually need an I2C level shifter for POX sensor (we don't, add 0 ohms across it and non pop)Add pads for I2C slew boostChange to a cheaper 12V AC adapter from aliexpress or somethingSwitch to fixed VOUT version of +3.3V buck converter, AND RUN and PGOOD signals togetherswitch to normal FET +3.3V discharge solution, with bleed resistorRecalculate UVLO and OVP thresholds on +12V Input sheetConsider lowering +3.3V local output capacitanceConsider removing +3.3V discharge holdup diode, replace with LED or MOSFETDouble check PGOOD LED gating, logic levels seem weird for what you're trying to doChange!Telemetryconfiguration to~Telemetryfor inversion bar in SCH textMakePOS5_USB_PGOODLED driver configurationALL, make it so that when an FTDI dongle is plugged in, this LED shines (POS5_USB_PGOODis driven high by dongle)