Schematics or Circuit Diagrams that aid learning.

FreePCB is a free, open-source PCB editor, released under the GNU General Public License. It was designed to be easy to learn and easy to use, yet capable of professional-quality work.

FreePCB – PCB editor

Some of its features are:

  • 1 to 8 copper layers
  • Board size up to 60 inches by 60 inches
  • Uses English or metric units (i.e. mils or mm) for most functions.
  • Footprint libraries courtesy of Ivex Design International Inc.
  • Footprint Wizard and Footprint Editor for creating or modifying footprints
  • Imports and exports PADS-PCB netlists
  • Exports extended Gerber files (RS274X) and Excellon drill files

Example – Logic Analyzer: This is an open-source logic analyzer called MiniLA contributed by Bob Grieb of the User Forum. The image on right is the Logic Analyzer PCB.

FreePCB - PCB editor

Some Features:

  • Up to 32 channels
  • 128 Kb of memory for each channel
  • Sampling rate up to 100 MHz (timebase in 1-2-5 sequence)
  • Input levels compatible with 3.3V and 5V logic
  • Selectable pretrigger/posttrigger buffer size in 8K step

Amplify uV from Sensors to mV levels for A/D Converters, which in turn may drive a display or connect to a uC means MicroController.

I have my own human interface and memory limitation. I am like a 8086 based nobody’s computer in a Penta-Core 5 Ghz Fiber-Computing World, add a 5 Teral Byte HDD. I am Obsolete, i am Legacy.

Now getting back to Bizness, the inputs from the world we interact are analog, A uV level from a Strain Gauge to measure Weight/Pressure; mV from a K Type Temperature Sensor or mV from LVDT Displacement Transducer to Gauge measure linear displacement. All these Low voltage/current, AC/DC need some signal conditioning and special construction – FOR – Amplification, Attenuation, Noise/Pickup Immunity/Rejection, Linearizion, Isolation and Transmission (long wire/wireless).

Thermocouple Amplifier Standard

This means take a small signal sample in the best possible way. The Sensor/Transducer shape and sensing/converting element/technology is chosen/developed. This low mV/uV is then Amplified/Cleaned and Transmitted.Some steps like Linearization can be done by software not all steps. Now we have a nice 0-10 V or 4-20 mA Signal which any A/D with process enthusiastically. The Digital signal will be eagerly processed by a uC with firmware, without batting a eyelid or like the kids say “look no hands” (then its plaster of paris for a few weeks).

This was a National Semiconductor Application Note, now TI. – Low Cost IC Stereo Receiver.

AN-147 Low Cost IC Stereo Receiver

Some Highlights

The LM3089 FM IF System does all the major functions necessary for FM processing, including a three stage amplifier/limiter and balanced product detector, as well as an audio preamplifier.

FM stereo demodulation is accomplished by the use of the LM1800 phase locked loop, thereby eliminating the need for external coils.

The AM function of the receiver is done completely with the LM3820 AM radio system. While designed for 3 section tuned superheterodyne application.

The LM382 dual preamplifier was selected for its minimum parts count and low noise capability.

Panel meters are employed in the FM system for both signal strength and center tuning, allowing for easy and accurate tuning. A directly driven LED offers immediate indication of FM stereo reception.

Low Cost AM FM Stereo Receiver

A single transistor tone control circuit was designed as the optimum cost/performance trade-off. The transistor is configured in a shunt-shunt feedback design, allowing gain variations between input functions.

The stereo power section, consisting of the LM378 dual audio amplifier, delivers 3W/channel with total harmonic distortion (THD) less than 1% and 4W/channel with THD less than 10%,

This indicates like LM3914 in dot-mode. It is a drawing i made made to troubleshoot a gadget, around two decades ago. Strangely it had a echo of a design i had made into a 7107 dpm years before that. Now i am scanning all my drawing and notes, useful or not. Clean or with errors. Many Errors = 1 Blunder. Some projects i made have been expensive Blunders. So see them with a skeptic eye, fix them, try them. Thats all for now.

See the Circuit Full Size – Microohm Meter with LED Analog Bar

Microohm Meter with LED Analog Bar

This has a 9V battery power. The 555 spins and a negative voltage for Opamp is created. This is a Low Offset amp of OP37 of Precision Monolithics, Inc PMI an early innovator. This diff-amp amplifies the uV of a 4 wire resistance measurement.

Now the current pump is the 2N2222 you see above the OP37. The FET and 555 do synchronous rectification. The LM324 is the Indicator and Analog to LED Dot-Bar Converter. The probes are Gold Plated, or use solid gold pins if you have them in plenty.