Home Page > Papers & App Notes
The following documents from the SR Library may be of interest. Some of
the papers and code review topics of general interest, while others discuss
specific SR equipment.
This paper describes techniques for interfacing electronic equipment with
different input and output voltage ranges together. Theory and circuits for
changing the range and offset of analog signals is reviewed, including passive
2 and 3 resistor designs as well as basic op amp techniques.
These techniques are useful in real life for interfacing sensors with one
voltage range to data acquisition equipment with a different range. While not
particularly difficult, the theory for many of the circuits is interesting.
Subjects like scaling and projective transforms even prove to be useful.



Written by Giovanni Rapagnani of the Royal Observatory of Belgium, this
paper describes the steps required to configure and connect a Meinberg C600RS
DCF77 radio clock so it can provide accurate time stamp information to the SR
USBxCH data acqusition systems.
The DCF77 longwave (77.5 kHz) radio signal with timing info emitted from an
antenna in Frankfurt, Germany is received by the Meinberg radio clock. The
benefit of using this radio signal is it does not require sky view and works
even when installed in the basement of a building. The DCF77 signal is only
available at locations within 1900 km of Frankfurt.



Written by Jeff Thorson of HenryThorson consulting, this paper describes
the analog filter response of the BurrBrown ADS1210 chip used on the SR PARxCH
data acquisition systems. The ADS1210 is a secondorder sigmadelta A/D
converter incorporating a threestage lowpass filter which defines the analog
system response.
The modulator, lowpass digital filter, and decimation stages of sigmadelta
converters are discussed. Their theoretical response is also compared
experimentally with measured responses to squarewave and trianglewave analog
input signals. The concepts described here are applicable to all sigmadelta
converters including the ADS1255 used on the SR USBxCH.



A precision sine wave generator program suitable for use with D/A converters
hooked up to a DSP32C digital signal processor is reviewed. While simple in
principle, precision sine wave generation requires careful programming.
Low precision methods for generating a sine wave include table look up,
interpolation, and incremental methods based on the addition formulas for sine
and cosine. But these result in tables of considerable size, interpolation
noise, or accumulated incremental error. Better solutions are discussed.



This zip file contains a sequence of programs developing code for the Fast
Fourier Transform ( FFT ). The programs proceed from a simple recursive FFT
function, onward to a production level radix 2 algorithm. All examples are in
standard C source code.
Customers are welcome to use these routines for custom programing in their
applications. Executables are for standard x86/DOS architectures. Recompiling
for other platforms is straighforward. The final radix 2 FFT does not use any
C runtime library functions, but does expect floating point arithmetic to be
available.
See the readme.txt file for a description of the algorithms covered.



