ELECTRONICS - [BK1786B supply] - [hardware addon] - [page 3/4]
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The image below shows my complete schematic for this project. You can click it to increase the size or you can download it as a PDF.
The circuit should be powered by a stabilized 12 VDC voltage. Other input voltages are possible but then you may need to add some additional components to the circuit. Also be aware the pin #4 of the DB9 connector is connected directly to the voltage input of this circuit. It is used to power the IT-E131 adapter that comes with the BK unit.
A 7805 controller will generate a stable 5 VDC voltage, used to power the microcontroller and the MAX232 IC. Some capacitors are added to remove the high frequency noise.
This electronic circuit is based on a PIC 16F628A microcontroller. I have chosen for this microcontroller because it has a hardware USART (Universal Synchronous Asynchronous Receiver Transmitter), necessary for the RS-232 communications.
The UART expects TTL signals (0/5V) while the serial communication works with +12/-12 V signals. So an adjustment of the voltage levels needs to be done. This is the reason I've added the MAX232 to the circuit: it will convert the voltage levels. The MAX232 needs a few 10 µF elco's to work properly, they act as charge pumps. (see the datasheet for more details).
The microcontroller itself is operated by a 19.668 MHz crystal. I have chosen this value because it is a perfect match for the baud rate of the serial link: The baud rate of the BK unit set to 9600 (9600 x 2048 = 19.668 MHz).
The circuit has 4 output LEDs and one output buzzer:
There is a 220 Ohm resistor places in series with the LED, to restrict the current through the LED. The maximal output current is approximately 14 mA, which is far below the maximal output current of the 16F628A microcontroller (25 mA/output).
In my circuit the buzzer is controlled by a FET (BS170), but it can be replaced by a regular transistor like the BC547.
Copyright ©1998-2022 Vanderhaegen Bart - last modified: August 24, 2013
