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This PCB is for microcontroller module with RS232 connector, transceiver, 3.3/5V voltage regulator and in application programmable 28-pin PIC. Module fits into breadboard or standard DIP32 0.6in socket, supports two most common types of DB9 connectors, parasitic power from RS232 and CPU voltage is configurable via solder jump. Sale is for PCB only, see schematic for more details. Buy only if you understand text below as we cannot help you build it nor provide support for this item.
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As the bare minimum, the circuitry around U1 is installed. This will provide
a RS232/UART converter.
The voltage regulator U2 collects power from RTS/TXD/DTR signals via D1/D2.
This will work only when one of these signals is on. RS232 specification
allows minimum 3V, but most usual are 5 (USB converters) or 12V. There must
be at least 5V from the serial port in order to collect enough power.
When relying on parasitic power, the MAX232
or derivatives is not most suitable for the job, since it requires 8mA for
operation (3-5mA other derivatives). If you are going to use this device with
parasitic power, use MAX3232,
which is pin compatible replacement with wider voltage range and requires only
0.3mA for full operation. However, if you will provide external power, the 8mA
part will be just fine. Just do not forget that some parts need 1uF capacitors
while others will work with 0.1uF.
The microcontroller can be any SOIC28 type PIDC16/PIC18 that has VDD/VSS/RX/TX/MCLR
pins compatible with PIC16F886-I/SO
If you will be running on parasitic power, lower-power part will be more suitable
and do not expect to get full 16 MIPS out of it. The design provides VDD/GND/RX/TX
signals + 16 I/O pins on the headers. Also there is an extra 3 pins beside RB7 that
provide ICSP port for initial flashing (not meant to be populated by headers).
There is room for modification - for example the unconnected portion of D2 can be used
for unregulated external voltage (e.g. 12V) up to 0.2A - use 10uF electrolytic cap as
C1 in that case..
This revision requires jumper on bottom side as shown below.
No parts are critical and you are welcome to use drawer parts you have
on hand. For example in the prototype we substituted C1,C8 and C9 by
through-hole parts, LED1 was PLCC2 part we already had. See our prototype
below. It should be also easy to mount TO92 version of LM317.
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