#12's Blog

I posted this to respond to a question, but it's good, so I blogged it. In air conditioning language: The labels you will find inside the machines are the first letter of the alleged wire color in comm use in, "The Trade". Green (G) is the interior fan command. If 24 VAC, then fan. Yellow is...

It has been interesting. My usual attention span for a new hobby is about 3 years. I spent nearly 4 years at All About Circuits. In that time I achieved over 11,000 posts and more, “likes” that anybody else (at that moment in time). I think I lowered the standards of the site in a good way. I...

I did this some time in the 1980's. Originally intended as a flashing light controller for advertising, and run on batteries charged from a solar cell. It is supposed to be a night detector that is fairly immune to the headlights of passing cars. The batteries charge in the day time and it...

A recent comment prompts me to list the basic fan laws here. For a given change in RPM, CFM2/CFM1 = RPM2/RPM1 Static pressure 2/ Static Pressure 1 = (Rpm2/ RPM1)^2 Horsepower 2/ Horsepower 1 = (RPM2/RPM1)^3 Reference: Trane Air Conditioning Manual, Page 270, The Trane Company, Fifty-Seventh...

There are accepted standards in this world. This goes directly to the definition of, "convention". A convention is an agreement among people such that, "This will be what we mean when we refer to that". For instance, the conventional flow of electricity is from positive to negative. That...

Tracecom and I got together on this. I designed it, he built it, he says it works. The Max6035 chip in 1/2% accuracy is used as a stable 10.00 ma current source. The rest is calibration and a Kelvin connection. The 200 mv scale on a DVM will show 199.9 while indicating 19.99 ohms. Good for...

Low Temperature Drift jfet Constant Current Circuit You can almost see by looking at the transfer curves of a typical jfet that all the curves for various temperatures cross at a point. My point here is that they really do cross at a point. Any particular part number for a jfet will have a...

Annoyed by the inaccuracy of people saying, "It takes six tenths of a volt to turn a transistor on", I did a graph of a bipolar transistor (2N4250A) to see what happened. The graph shows an almost perfect straight line from 1na to 1 ma on a lin/log graph. (I quit at 1 ma to avoid heating the...

This thermostat has been in service since January 14, 1980 and has never needed a repair. Even the aluminum electrolytic (capacitor) on the power supply has not failed! The "real" one drives a triac for the output (short sighted of me to do that.) If you set the hysteresis with any...

This is an LM723 used as a floating high voltage regulator. Same cautions as blog#4 apply AND there is no common mode input range listed on the datasheet so it might not adjust down to one tenth of the maximum output voltage. It's rather difficult to design a feedback loop for 1000 volts, so I...

This is a much easier to read schematic of Fig. 22 in the LM723 datasheet. It illustrates the connections required to get a regulator circuit to "float" on the output voltage. This one is designed for 1000 volts with a 50 ma constant current circuit. Caveats: The MOSFET will dissipate 50...

I built this circuit while studying 1/2CV^2 = 1/2LI^2 The transistors I had were RCA brand 1B05 and the diode is a 2000 volt fast Trr diode. Set the current by adjusting Vcc. I used a single function generator to get a ttl square wave to allow current through the inductor under test, and...

I saw this information on this site and decided to "blog" it so it would be easily available in the future. It is about the turn on time of the diodes and was originally posted about a snubber question. \begin{array}{l|c|c} Time & 1N4001-5 &1N4006-7 \hline .2 usec &.1A& .3 usec...