Tech Forum

Mr. Lambdin inquired about a circuit to monitor the AC ripple on the output of a linear power supply.  The inference is that the frequency response of the circuit need not be excessive. He also wanted a digital display.

I found what ought to be a suitable device, in kit form, from Amazon, for $29.95. See https://www.amazon.com/Oscilloscope-Handheld-Pocket-size-Electronic-Learning/dp/B01LWK49W3/ref=asc_df_B01LWK49W3/?tag=hyprod-20&linkCode=df0&hvadid=309778489815&hvpos=&hvnetw=g&hvrand=18068906155916055584&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1018200&hvtargid=pla-465542683176&psc=1

In a linear supply the vast majority of the ripple will be at the input frequency which will normally be the power line frequency (50 or 60 hz) or two times that frequency (100 or 120 hz.) A digital multimeter on the AC volt ranges is intended primarily for that frequency range. By blocking out the DC from reaching the meter any DMM set to the AC volt ranges should measure it fairly well. A "True RMS" type meter is best since the ripple probably will not be a sine wave.

To block out the DC part simply put a capacitor in series between the positive side of the supply and the positive input of the DMM. A value of 1 microFarad or more should work. If you use any type of polarized capacitor such as an electrolytic make sure to connect the positive end to the positive output of the supply. Of course, make sure the voltage rating of the cap is higher (16 or 25 Volts should be fine) than the supply. You may need to put a fairly high value resistor (say 10 K Ohms) across the meter leads (from the negative end of the capacitor to the negative side of the power supply.

I have spent a lot of my life wondering about magnetics. Welcome to the club! Hopefully the information that I have is correct

Here are a few basics:

  1. When an electron moves, it generates a magnetic field in addition to the electric field that's always there.  — Why?: Because
  2.The field exists if the electron/electrons move in a wire, a stream (e.g. in a tube), or anything else.
  3. Magnets 'work' because (if I have this right), the arrangement of their molecules is such that the electron orbits of the individual atoms are oriented such that the fields generated add together. The relative strength of a magnetic material is based on how well they are aligned. Magnet discussion usually describes magnetic domains within the material. (Magnetizing a material means that you apply a magnetic field to align the domains.)
  4. Non magnetic materials don't feature this alignment. Electron orbits are in random orientation and the fields cancel.
  5. Magnetic fields are constant for DC current and non moving magnets.
  6. Time varying fields are generated from AC current and moving magnets.
  7. Time varying fields do the following: A. If they pass through a wire they will cause the electrons to move — thus a transformer. B. If they encounter another magnetic field they will cause either an attractive or repulsive force — thus a motor. (This force is also present in static field interactions, but that won't make a motor.)
  8. Coils of wire are used in transformers and motors because the fields add and compact devices can be made.
  9. The field descriptions are always confusing. What I got out of it was that the B field is the description for the field you would find due to the current or magnetic material. The resultant field that you can measure depends on the material that the field is in.

Exmple: If you have a long solenoid, the field inside will be fairly constant if you're not too close to the ends. If you put a piece of ferrous material inside, there will be an increased field through the metal because it's easier for the 'flux' to go through this material. (This also affects the input current to some extent, in the same way that a a lower resistance load affects an electric circuit.)

  10. There seems to be no end of magnetic units — just like farenheit, centigrade, and Kelvin for temperature.
  11. Maxwell hopefully understood his equations, along with some other smart people.

The math that you see everywhere generally shows what fields you can expect due to different circumstances. It is very difficult, and I certainly don't understand it. Happily, computers are now available that are powerful enough to avoid a lot of it. They use a method called finite element analysis. Basically they calculate fields based on the sum of tiny elements at each point of interest in a field.

I really hate to be a wet towel, but this is really not a good idea. Arbitrarily adjusting things like fuel and timing is most likely to result in a smoking, noisy engine. If run to long the engine is more likely to self-destruct than increase power. Not to mention tailpipe pollution. Even "professionally" reprogrammed engines emit excess pollution, and shorter lifespan.

A Passive Infrared (PIR) detector is much less expensive and easier to use. There are many available for outdoor use, with battery operation and remote monitoring by Wifi or other means. I don’t know of any DIY road loop circuits, and they are being phased out due to high installation and maintenance costs in favor of cameras, which are another choice.

I once bought a little board from a guy in Australia which monitored standard NTSC video and detected movement. Worked pretty well.

I would suggest an ebay search for guitar tune”. There are several listed in the ten dollar range with free shipping. The tuners don’t generate a tone but receive a tone and show the note on the lcd. I think parts cost for self build would be higher than purchase.

Make a long distance microphone like they use at football games. Mount a microphone at the focal point and connect to an audio amp and headphones.