This schematic of a 60 Hz 555 timer based circuit was submited by Jamie Morken for people who want battery operation or to place the AtoD at the sensor location. It is written for the seismometer project proposed for the Amateur Scientist column of Scientific American. This program is distributed as Freeware and may be used or modified by anyone for non-profit enterprises. If modifications are made you should completely document these changes in the source code before redistributing the software. The designation of Freeware does not in any way relinquish the copyright of this program to others, and only implies that the program is distributed without charge.
Inputs are single ended, that is, referenced to ground.
The max186 may be run in single or bipolar modes. In single polar mode only a 5V supply is needed, but signal input voltages cannot swing negative. Inputs to the MAX186 should be tied to ground with a 100 kilohm resistor to avoid interference between channels. The forth channel is used for timing. The main requirement is that the parallel port operate in a similar fashion.