|Subject:||Re: [Paparazzi-devel] Tiny v2.1 - PCB files and Components list|
|Date:||Thu, 25 Oct 2007 07:29:14 +0200|
Hi, i have made similar things.
- J17 (IRH) change the 4pin header to 5pin header like ADC0, this eliminates the need
for a 4pin header.
- LPC_RESET add this signal to the download header.
- 4017 The supply should be connected to 5V in order to make it compatible with all servos,
not only JR and some others.
- GPS_RESET max voltage is 1,95V . I recommend
using a open drain pin (output on gnd, otherwise input) to drive it.
For merging BOOT and GPS_RESET, i suggest a diode in order to protect the GPS
from user download socket. Don´t forget a 10n cap. Don´t make programmer errors or
the gps module become damaged. If you connect the GPS_RESET to the LPC_RESET as
described below, merging boot and GPS_RESET don´t work.
- GPS Connection from V_ANT to GND is wrong. Leave unconnected if not used.
Connect VCC_REF and V_ANT with a 10 Ohm resistor.
Note that this resistor must be 1/4 Watt, the normal 603 resistors don´t work.
This is for active antennas (3.3V, 5V designs don´t work) or it´s possible to don´t
popolate it, or to drive it by SW.
- GPS add a testpoint or solder jumper to BOOT_INT in order to possibly recover from a
wrong or failed firmware update.
- GPS/LPC_RXD0 add safety resistors, in case of both GPS and USER drive the pins, ie
GPS_RESET is not driven low or the low driving signal is too high (gps require low <0,65V , LPC <= 0.8V).
- GPS EXTINT0 shoud be used, example: LPC214x drives the camera and at the same time triggers
timestamp from gps, that is logged, included the gps position.
Maybe isolated with a resistor, that can not be placed or eventually desoldered.
- GPS TIMEPULSE should be used, specially when the gyro module with a own processor is used,
in order to timestamp the single ADC readings and as another case to check the osc long term stability.
- GPS/LPC VBAT from LPC and GPS should be connected. This allows holding a (checksum protected)
ram portion as logging (usb memory as example, if usb is not used in flight), that
allows having a history, if somethings goes wrong. At the same time, if there are
problems with the main supply, some spikes or ground bouncing from the servos,
with the VBAT used, one can be sure that the ram contents is ok.
- GPS GPSMODE should be adjusted, either (12/6/5) 1/1/1 or 1/0/0
- GPS Reset As Note, reset can be triggered by SW, without the need for a HW pin.
- RESET strategy: The GPS has a internal 2.4V voltage supervisor. If the GPS module is
connected to the 3.3V using a 0.3V drop diode, the voltage supervisor could be
used for both, the gps (2.4V) and the LPC ( 2.7V). Maybe consider improving the
reset line from GPS by pulling a external resistor and cap between the reset and
the vdd18out line. (cap naturally to GND).
Note: The LPC reset voltage must be above 2.0V, this implies a sort of level converter.
- Powering: It can help, if the analog VCC and the GPS VCC came from a 3V LDO connected to the
3.3V VCC rail. Further the 3.3PSU are located a bit distant from the GPS module.
Using a 3.0V LDO can be the same as using the 0.3V drop diode for the voltage monitor.
- GOLDCAP add the possibility to use a recharcable battery instead of the goldcap.
It´s not so easy to find goldcaps rated for higher temperature.
- GPS / GPSMODE design for the possibility to use the cheaper A module.
- SUPPLY: the PSU must be checked, if the VOUT could be at higher voltage than VIN.
Othervise protection diodes must be added to the desing.
- USB-Led add a led after the T3 resistor in order to have a feedback when the USB is activated.
This led don´t need to be populated, but it´s nice to have it.
- USB hotplugging Protection diodes are needed for hotplugging.
For the same reason, 100 Ohm resistors should be plugged on the button, led3 ... lines.
- supply Analog and digital GND/VCC should be layouted separatly and merged in one point.
- Supply Add a 603 resistor before the inductance. This could limit the interference and can
be substituted with a ferrite bead.
- POWER Seeing the DC/DC converter, use the Inhibit. This can be used to dont´ allow power-up
the thing, if the battery voltage is too low. Further, add a switch to the LCP and
Inhibit with a OR (two diodes) borren from VBAT_MEAS and one line from LPC.
In this case, one can power up the thing like a cellular phone.
On power up (power line pressed) the LPC sets the own power line high in order to
remain powered. If the button is pressed for a long time, the LPC powers off itself.
Shorter button pressing could be used for takeoff, abort signaling and similar.
- LAYOUT: Check the lea integrations guide for dividing the analog section on the board with
the RF emitting digital section as MCU´s and similar. This increases the size of the board,
but it helps a lot for having a better GPS solution. I prefer having the GPS on it´s own board,
maybe combined with the infrared sensors.
- LPC214x The ground plane is a bit missing. With some more hand-Layout it´s possible
to have more ground plane below the MCU.
- Grounds between servos and MCU, especially GPS should be divided. Think of current measuring
of the servos using a resistor between the MCU`s ground and the Servos ground (including cap)
in order to measure the current of servos and automatically reduces a bit the ground bouncing.
- TVS Adds some TVS devices, for the GPS antennas, there exist extra devices. Required for EC compliance test,
because the GPS antenna input is not 20K safe.
Further, TVS could help with the ground bouncing problem when using the current sensor
because this behaves like filters on certains situations. Spice simulation is suggested.
- Temperature: Add a internal thermistor or temperature sensor (i2c) in order to sense the own temperature
Further, on the power connector, add a pin for a thermistor sensing that either can be used as thermistor
or 1-Wire interface for cheap smart-battery controller.
- Power after adding the power logic in order that the board can be power-on or off by SW, add
the possibility to power only the logic from the USB, excluding the servos.
This allows powering the uav externally from the usb port (modem, gps, micro) having
a sort of standby without using the main battery or for HIL simulations without consuming battery.
- AUX It will be nice, if a high power led or buzzer or something similar can be switched
on indipendently of the payload. This needs only a additional transistor connected
to the 5V rail (not 3.3V) and naturally two resistors.
- I2C mem Add a I2C memory to the PCB. This allows logging external sensors without needing extra payload cpu.
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