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README.md

README.md

#256 Pease

A Bob Pease tribute, LM331 voltage-to-frequency kit from The Boldport Club (Project #1).

Here's a quick demo video to show it works..

Build

▶️ return to the LEAP Catalog

Notes

The Pease is a tribute to the legendary analogue designer Bob Pease.

'My favorite programming language is... solder' –Bob Pease

It is another beautiful PCB from the Bolport Club, and is a great excuse to find out more about the featured chip - the LM331 voltage to frequency converter.

I joined the Boldport Club rather late, and missed out on the original Pease kit (now out of stock). But I did manage to snaffle the PCB in sale of "Just Less the Perfect" boards. Sweet!

Pease_board_front

About the LM331

Although the LM331 is used here in its basic voltage-to-frequency converter mode, it is actually quite a bit more versatile, with applications in:

  • Voltage to Frequency Conversions
  • Frequency to Voltage Conversions
  • Remote-Sensor Monitoring
  • Tachometers

See the LM331 Datasheet for more.

Kit Modifications

Since I was kit-less, I decided to experiment a bit. Firstly, I'm using a 20kΩ LDR for input rather than a phototransistor. Secondly, after testing the original circuit on a breadboard, I decided to slow down the frequency.

  • the original runs at hundreds of kHz, so acts like a PWM LED dimmer
  • I pulled the operating frequency down to 4-10 Hz, so it visibly blinks

The end result is a light/voltage controlled "blinky". Depending on the potentiometer trim, it will:

  • stay "off" in bright light
  • start to blink at ~10Hz with a very low duty cycle (~1%) as light levels drop
  • blink hard at <7Hz with high duty cycle (50% and over) in dark conditions

The specific component changes (with reference to the schematic below):

Ref Original Replacement Rationale
R6 330Ω 220Ω a brighter LED
R1 6.81kΩ 1MΩ massively reduce base frequency
C1 330pF 100nF massively reduce base frequency
C2 1nF 1µF achieve greater duty cycles at the reduced frequency
S1 Vishay BPW96C Phototransistor 20kΩ LDR ..because I didn't have a phototransistor on-hand

The particular LDR used has a range of about 200Ω (bright light) to 20kΩ (dark).

The component selection means the board works happily from 5-9V. I repurposed an old mouse USB lead as a 5V USB power supply connector for the board.

The Build

No unboxing this time - a pity, as the original kit packaging looks really neat.

Testing the circuit on a breadboard to experiment with component values..

build_breadboard

Final component selection..

build_components

Build complete, front:

build_complete_front

Finished, around the back...

  • hmm, still trying to get perfectly round globules of solder.
  • Hot glue to the rescue for securing the USB power connector. Is that allowed on a Bolport Club kit???!

build_complete_back

Performance

Obviously, ambient light conditions and the trim of the pot alter the circuit performance, but here are some scope traces for roughly "light" and "dark" situations.

Bright Light - Original R/C components

High frequency 175kHz; duty cycle ~40%

scope_original_light

In Darkness - Original R/C components

Frequency reduced to ~ 30kHz, and duty cycle over 80%..

scope_original_dark

Bright Light - Replacement R/C components

Low frequency 9 Hz, and low duty cycle <5%

scope_revised_light

In Darkness - Replacement R/C components

Frequency reduced to ~4 Hz, and duty cycle over 50%..

scope_revised_dark

Construction

Breadboard

Schematic

Build

Credits and References