131 articles written by Jim Keith

Author: Jim Keith

About: I grew up in Massachusetts. I cut my teeth on electrical cord and learned how not to splice such by age 7. Started building my first hobby circuits at age 11 using the venerable 1N34A diode & 2N107 transistor. In high school, I knew more than the teacher so I taught my physics class electronics--LOL. Still too dumb to get into MIT, I attended Wentworth Institute of Technology (where MIT dropouts also go) and then Moody Bible Institute. However, most of what I learned was not in school. I eat, drink and sleep circuits--repeatedly, have I awoken with a circuit solution. The electronics industry has provided good employment throughout my career and now retired, I continue with hobby stuff and a small ebay electronics business. The photo is that of Toby, my grandaughters' beagle.


Unijunction Transistor Flasher

Unijunction Transistor Flasher

Jim Keith - 03/02/2015

Using the rather dated 2N4871 unijunction transistor it is possible to make a simple, but very bright, daylight [...]
36V Battery Level Indicator circuit

36V Battery Level Indicator

Jim Keith - 01/12/2015

This battery level indicator offers (5) LEDs that light up progressively as the battery voltage increases. This is [...]
Apollo Guidance Computer

The Apollo Guidance Computer

Jim Keith - 01/09/2015

Most of us remember clearly where they were and what they were doing on days marked by world-changing [...]
AT89S52 Minimum Development Board Schematic

AT89S52 Minimum Development Board – 8051 Tutorial #2

Jim Keith -

Dirt cheap hardware is available for developing 8051 microcontroller applications. Such is well suited for students and budget-limited [...]
LM339 as an Op Amp

What is the difference between op amps and comparators?

Jim Keith - 01/02/2015

While both operational amplifiers and voltage comparators have been with us since before 1970, the similarities and differences [...]
SCR 12V to 5V USB Converter Schematic 3

SCR 12V to 5V USB Converter

Jim Keith - 12/23/2014

SCRs are the switching devices for this unusual DC to DC converter that is suited for the ubiquitous [...]
Edge Triggered 555 Monostable Schematic

Edge-Triggered 555 Monostable Multivibrator

Jim Keith - 12/12/2014

While the 555 oscillator IC is a very versatile device, it can also be quite tricky and solutions [...]
Microcontroller Photos

8051 Microcontroller Overview & Hardware – Tutorial #1

Jim Keith - 12/07/2014

The intel 8051 series 8bit microcontroller, originally introduced in 1980, remains popular and has had perhaps the longest [...]
Clap Switch circuit schematic

Clap Switch Using Latching Relay

Jim Keith - 12/04/2014

This is a simple clap switch circuit with high sensitivity. The only unusual component is the single coil [...]
SCR DC to DC Converter Evaluation Circuit

SCR (Reverse Blocking Thyristors) DC to DC Converter

Jim Keith - 11/24/2014

Two series SCRs (reverse blocking thyristors) are unlikely switching devices for this DC to DC converter. This topology [...]