Can you use voltage dividers as regulators? What if you add a Zener Diode? In this AddOhms episode, I show what happens when you try to power a complex circuit like an ESP8266 with a voltage divider instead of a regulator. (Spoiler: Get a voltage regulator.) This video tutorial is related to a write up I did recently on Zener Diodes. For questions or comments visit the AddOhms Discussion Forum.

Behind the scenes

A significant change for this AddOhms Episode is that I moved from Final Cut Pro X to Premiere Pro. I also shot the entire video in 4K, even though the output is 1080p. Animations were still done as 1080p compositions. One snag I ran into, the color corrections I applied in PPro, didn’t seem to get exported. You might notice when the breadboard is on screen, it has a very slight yellow tint to it.

I’ve been changing how I produce the videos. It’s shortening the cycle time. The key is that I’m not trying to animate every scene. The amount of work involved is just too much. I animate practically every frame. So in a 6-minute video, that’s just too much.

By the way, there are two easter eggs in this episode. Can you find them?

Voltage Dividers as Regulators on YouTube

Op Amp Circuits by Bob Pease

TI (Formerly National Semiconductor)
September 2002

TI AN-31 Torn Paper

Op amps are one of the most versatile ICs in electronics. A purely analog device, they can be used for amplification, summing, integration, and a whole host of other circuits. AN-31 from Texas Instruments is 32 pages of op amp circuits. (Note: this document was created before TI acquired National Semiconductor.)

Even more amazing is that the author is Bob Pease. If you never heard of Mr. Pease, please spend a few minutes right now reading this TI page dedicated to him. His contributions to electronics are nearly immeasurable. (Sadly, he was involved in a car accident after attending the funeral of his equally famous engineering friend, Jim Williams.)

Download AN-31 from TI

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Zener diode makes for a lousy regulator

Reference and regulation are not the same thing

zener diode regulator

The Zener diode is often used to create a reference voltage. In tutorials and even college texts, there are mentions of creating a Zener diode based regulator. The idea is that the Zener maintains a known voltage drop. The problem is that current matters. This post looks a quick Zener diode overview and shows what happened when I tried to power a microcontroller using a “Zener diode regulator.”

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5 Voltage divider circuits that go beyond dividing

voltage divider circuits

Here are some ideas of what you can do with the humble voltage divider. This elementary circuit has a few inventive uses. To be upfront, one of these uses is NOT as a voltage regulator. If you need a voltage regulated, get a voltage regulator! At some point or another, I’ve built all five of these voltage divider circuits. For me, the voltage level shifter is the most common.

  1. Measure Battery Voltage
  2. Signal Level Shifter
  3. Reference Voltage
  4. R-2R Ladder
  5. One Analog Input with Many Buttons

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Pi Cap Hands On Review

My first impressions of a Raspberry Pi capacitive touch hat

Pi Cap Review

The Pi Cap adds capacitive touch buttons to your Raspberry Pi. Bare Conductive was kind enough to send me one. I do not have a project in mind right now, so here are my first impressions.

What is the Pi Cap?

Arduino tends to call daughter cards shields, while the Raspberry Pi community calls them hats. The Pi Cap is a hat. It plugs into the GPIO header of a Raspberry Pi and provides 13 capacitive touch pads. There is a traditional push button, an LED, and a prototyping area. While the Pi Cap does consume all of the GPIO pins, several are broken out near the GPIO header.

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The first part of the tutorial looks inside of a Brushless DC Motor, or, BLDC. Then I show a discrete transistor circuit that can drive one. Of course, you’ll need a Microcontroller like an Arduino to drive it! Lastly, I briefly talk about an ESC.

Overall, a BLDC is better than a Brushed DC Motor (talked about those on #20) because:

  1. There are no brushes to wear out
  2. No sparks when the motor spins
  3. You can get way faster RPMs out of a BLDC.

Check out the AddOhms #21: Brushless DC (BLDC) Motors. Show notes are available here.

Supplyframe Hardware has published a video of a talk I gave in July 2017. This talk was at HDDG 22. The focus of my discussion was how an oscilloscope’s trigger circuit works. I built on that and talked about some of the behind-the-scenes stuff of what is going on with a digital oscilloscope. (You can download my HDDG 22 slides here.)

PWM a 3-pin PC fan with an Arduino

Note: 4-pin fans already have a PWM signal

Aeroscope Measuring a Fan

A question came up on IRC regarding how to PWM a 3-pin PC fan with an Arduino using analogWrite(). Controlling the fan was seemingly straightforward. The problem was that the hall effect sensor, or TACH signal, was incredibly noisy. The noise made it impossible to measure the fan’s rotation. Working through the question, I found three issues to tackle:

  1. You need to use a PNP transistor
  2. Filter capacitors help
  3. Create a non-blocking RPM measurement (with millis())

This post addresses all three issues regarding how to PWM a 3-pin PC fan with an Arduino.

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During #22 of the Hardware Developers Didactic Galactic meetup, I discussed Oscilloscopes. (Previously James talked about capacitors.) In the presentation, I broke down the internals of an oscilloscope. The presentation started off with a block diagram. Then I discussed the main components: vertical amplifier, A/D, memory controller, some of the computer side stuff, and the keynote was on triggering.

The trigger circuit of an oscilloscope fascinated me since very early in my HP/Agilent career. When I saw trigger modes like Pulse, Violation, Rise Time, and “Runt,” I thought: Wow, this must be the most complicated circuit in the scope! While it isn’t trivial, it very clever how just a few pieces of (relatively) simple hardware drive one of the most important aspects of a digital scope.

Download Slides

Rick Altherr also gave an excellent talk on ECUs and their sensors. (I always thought ECU only meant engine control unit. His talk helped me understand why that isn’t really the case anymore!) It was great to learn about the combination of the engine mechanics with the electronics that control it. !)

See Rick’s Slides

Raspberry Pi Startup Script Tutorial

Part 3: Pi Soft Power Controller, what to put on the Pi

raspberry pi startup script

The last couple of weeks I have been making progress and posts on my RetroPie build. I’m putting a Raspberry Pi inside of an actual SNES (well Super Famicom). Part 1 covered the schematic for a Soft Power Controller. In Part 2 I broke down the RPSPC state machine. This 3rd and final post of the series is a Raspberry Pi startup script tutorial. It covers how to make scripts run at startup and shutdown.

When I started researching how to make Raspbian run a script at startup and shutdown, I found a ton of links and questions asking for help. None of them helpful. Why? Because they were wrong. At least, they are now.

/etc/rc.d doesn’t matter!

It turns out, Raspbian Jessie does not use SysV for init (anymore). So it does not matter what you scripts you put in /etc/rc.d. Pretty simple but missed by many!

Here is a correct Raspberry Pi Startup Script Tutorial.

The Key is systemd

Once I started researching how to make systemd do what I wanted, new problems emerged. The syntax for systemd is not as straightforward as I first thought. Thanks to readers, I was pointed towards the RedHat systemd manual. After reviewing it, I was able to create a service that runs at startup and shutdown.

In the end, I was unable to prevent this process from running during reboot. There seem to be some more layers to make sure systemd knows the difference. In the end, I decided it was not necessary to avoid the reboot.

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