This simple amplifier shows the LM386 in a high-gain configuration (A = 200). For a maximum gain of only 20, leave out the 10 uF connected from pin 1 to pin 8. Maximum gains between 20 and 200 may be realized by adding a selected resistor in series with the same 10 uF capacitor. The 10k potentiometer will give the amplifier a variable gain from zero up to the maximum.
Posted on Tuesday, April 13, 2010 • Category: USB Circuts
We employ two UART boards in the course, one which can be connected to the serial connector of the PC (UART-RS232), and a second that can be connected to a USB port (UART-USB). The former is used in the lab and is part of the standard take-home equipment. The latter is part of the (limited!) number of take-home targets for students who are working on a Laptop without serial connector. In both cases, communication is done with the UART module of the microcontroller. In the case of the normal UART board, the MAX232 simply transforms the voltage levels to RS-232 standards (± 3-15V; in our case 12V, with LOW=+12V and HIGH=-12V). In case of the UART-USB, the FT232BM transforms the UART protocol to the USB protocol. This is transparent to the controller, which communicates over the normal TX and RX pins.
Posted on Tuesday, April 13, 2010 • Category: Audio DAC
The voice messages are recorded into the on-board microphone, then each message can be individually triggered by an external signal. The inputs can respond to simple electrical contacts, logic levels or voltages, and all inputs are debounced to prevent false triggering by electrical noise. Each message can be arranged to play once on a selected change of input state (high-to-low or low-to-high), or to repeat continuously until the trigger condition is removed. These options are selected by DIP switches.
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