A Measuring Instrument with an Optically-Isolated Analog Input

This was started in 2008 to use up a Basic Stamp II which had had to be replaced with a IIsx in the Stamp Cycler because the Stamp II had insufficient memory to store data. This was before I got the Secure Digital interface. However, there were hardware problems with a partial build, and I turned to other projects and put it aside for a year. Also, it had an ugly box.
In 2010, I decided to junk the ugly box and make a new one out of oak. It took a while, but I fixed its hardware problems and finished the hardware and reference software.
The design now features an optically-isolated analog input with a 50-milliolt range for measuring current. The earlier projects: Lab DAU, Stamp Logger and Stamp Cycler had bi-polar differential inputs, but these had less sensitivity and a limited common-mode range. For this project a unipolar range was considered adequate. Of course, being isolated, the inputs can be switched.
Other hardware includes a rechargable battery, an analog meter, a loudspeaker, an analog voltage input, and several digital inputs and outputs, including bi-directional. Timing is provided by a Dallas DS1302 time and date chip with its own re-chargable battery. There is also a Rogue Robotics Secure Digital interface. The display is a 16 x 1 LCD from a discarded fax machine. Control is by a rotary switch on the front panel, aided for setting by a momentary switch at the back.
There are three "bells and whistles". The loudspeaker can emit clicks and beeps by the Stamp II FREQOUT command, and a variety of door bell chimes using a kit. There is also an aircraft fault indicator, which shows a white or black ball, mechanically latched.
Due to the limited size of the Stamp II program space, a separate program was written to set the initial time and date into the DS1302. The values are written into files on an SD chip with a computer text editor. The main program can adjust by the hour for Daylight Savings time, and by the minute for drift. The Dallas chips never seem to lose the date, and its memory is put to good use.
The analog meter has switches to measure the current and voltage inputs after signal conditioning, as well as the main battery voltage. There is a built-in battery charger. I made my own DC-DC converter to power the isolated input. I wound the transformer myself. The current input uses a trimmed amplifier, an Op-07. The three optical isolators are HPCL7710, which has logic-level inputs and outputs. The two 10-bit serial ADCs are TLC1549s.
There are also 2 digital I/O and 3 open-drain outputs
The only change since 2010 was to replace the 7.2V battery with 6 AA cells.
These are photographs of this instrument and its accessories.
These are the system and circuit diagrams:
This is the main program

These are the setting program page:
RTC Setting Program