87 lines
3.6 KiB
Markdown
87 lines
3.6 KiB
Markdown
motoserial
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the motoserial is a phone controller
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it is used to power, flash, and communicate with Motorola C1XX phones
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the purpose is to use it for osmocomBB
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the USB interface will offer 4 UART ports, do communicate with 4 phones
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provide external power (4.5-5.0 V, ~2 A) so to be able to power the phone, but also be able to flash them
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purpose
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I used the osmocom baseaband software on Motorola C118 phones to monitor GSM networks
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to communicate with them, I used USB to UART converters (CP2102) on the 2.5 mm TRS jack
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to flash the phone with the osmocomBB firmware, remove and reinstall the battery, start osmocon (or leave it running), and press on the ON button to start the bootloader
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but sometimes the software gets stuck, and for monitoring GSM networks, an automatic way to reflash the phones had to be found
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technology
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instead of the ON button, a pin on the back of the phone can be used
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but I noticed that plugin the charger had the same effect
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and instead of the battery, a 5V power source can also be used
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so the trick is to use 2 transistors: 1 to simulate battery re-plug, and 1 to simulate charger replug; by switch off and on both power sources
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since they share the ground pin, p-MOSFET on the positive side had to be used
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actually the order and switching timing is not too important
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thus one transistor, switching both the battery and charger power sources, is enough (and a n-MOSFET can be used)
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the battery can be replaced by a regular 5 V power source, the same as the one used for charging
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if the voltage is above 4.2 V, the battery should not be charged
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to prevent power comming back on the power source if the phone charges the battery, a diode should be use on the positive side on the battery power source
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this would also decrease the voltage (due to the forward voltade drop of the diode) and bring it closer to the usual 3.7-4.2 V voltage level
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the phone cosumes at 3.7 V on average:
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- ~ 90 mA when idling
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- ~ 120 mA when receiving
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- ~ 220 mA when transmiting
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when transmiting, peaks of 2 A can be reached
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this can be lowered to 1 A when an 470 µF capacitor is used
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hardware
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========
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files
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-----
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motoserial-phone:
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the battery replacement
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provide 5 V (~1 A) input power
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the other port is to forward this power to the charger
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the PCB will replace and provide power instead of the battery
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a diode is used to prevent revers current when charging
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capacitors are necessary to cope with the peak power usage when the phone transmits
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motoserial-spare:
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this is the USB to 4 UART + power controller board
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it uses spare parts from my component stock (mainly the expensive FT4232H)
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version
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0:
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working version
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A:
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first scrape prototype built using CircuitPro + ProtoMat S63
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bugs:
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- the hole for the USB and header pins are too wide. I hope it would create some through hole plating thanks to capillarity, but it didn't
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- wider vias annulus would be a good idea
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- DTR it set (to low) when the serial port is opened, but is no reset (to high) when closed (FT4232H specific)
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- RTS can be reset to high on close, but that need to be programmed in the FT4232H's EEPROM
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- the 3.3 V on DTR can not drive the pMOS because it's switching 5.0 V, but V_GS < 1.1 V
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- decoupling capacitors on the serial lines should improve the quality
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- try if with less feritte beads and decoupling capacaitors PLL still works
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B:
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first cape prototype built using CircuitPro + ProtoMat S63
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bugs:
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- I used nMOS instead of pMOS, which won't work because the power connection on the phone shares ground with UART
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C:
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second cape prototype built, using CircuitPro + ProtoMat S63
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bugs:
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- one ground copper connection in the plane cut because too thin
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- 100nF dim the UART signals and should be removed
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