LCS-1M - A Low-Cost Hobby Oscilloscope
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| Design Overview |
The oscilloscope hardware has several main sections, described in the following pages.
First, there is the controller. It is the heart of the scope and is based on a industry-standard 8-bit
microcontroller. It sets up the scope's sample logic, sets the input amplifiers' gain and offset, reads the
captured samples from the capture memory, and communicates with the PC which tells it how to set up
the hardware and then waits for it to send back the acquired data.
The input signals are conditioned in the analog frontend, which depending on the signal levels either
attenuates them or amplifies them, and can also add offset. All this is necessary to make optimum use of
the fixed voltage range that the analog-to-digital converters can convert into digital information.
Third, the analog-to-digital converters (ADCs) take the analog signals and convert them into digital
numbers which then get stored in memory (static RAM = SRAM).
The sample process and sample storage is controlled the sample logic. It consists of a few generic
CMOS logic chips, controlled by the microcontroller, and are also used to read out the data from the
capture memory.
The PC interface is standard RS-232. The cable connecting the PC can either be a normal serial cable,
which is the cheapest solution (in this case the scope is connected to the computer's serial port, e.g.
COM1) or can contain an integrated serial-to-USB converter, allowing to connect it to the computer's serial
port. The change is transparent to both the scope and the PC software and has no impact on
performance, but is helpful because the old serial port is slowly disappearing from new computers.
Finally, the power supply circuitry converts the voltage coming from the external power supply - which can
vary anywhere between 8 and 15 V - into a stable and well defined voltage suitable for the circuit. This
voltage is also the reference against which the input voltage gets measured.
First, there is the controller. It is the heart of the scope and is based on a industry-standard 8-bit
microcontroller. It sets up the scope's sample logic, sets the input amplifiers' gain and offset, reads the
captured samples from the capture memory, and communicates with the PC which tells it how to set up
the hardware and then waits for it to send back the acquired data.
The input signals are conditioned in the analog frontend, which depending on the signal levels either
attenuates them or amplifies them, and can also add offset. All this is necessary to make optimum use of
the fixed voltage range that the analog-to-digital converters can convert into digital information.
Third, the analog-to-digital converters (ADCs) take the analog signals and convert them into digital
numbers which then get stored in memory (static RAM = SRAM).
The sample process and sample storage is controlled the sample logic. It consists of a few generic
CMOS logic chips, controlled by the microcontroller, and are also used to read out the data from the
capture memory.
The PC interface is standard RS-232. The cable connecting the PC can either be a normal serial cable,
which is the cheapest solution (in this case the scope is connected to the computer's serial port, e.g.
COM1) or can contain an integrated serial-to-USB converter, allowing to connect it to the computer's serial
port. The change is transparent to both the scope and the PC software and has no impact on
performance, but is helpful because the old serial port is slowly disappearing from new computers.
Finally, the power supply circuitry converts the voltage coming from the external power supply - which can
vary anywhere between 8 and 15 V - into a stable and well defined voltage suitable for the circuit. This
voltage is also the reference against which the input voltage gets measured.