Tag Archives: math

Is that Cuckoo a 1-day clock, or an 8-day clock?

Because of the economics of cuckoo clock repair, you can easily find old, dirty cuckoo clock movements on eBay for a fraction of what a new movement costs. These movements come with no documentation, so you get to work out which chains, weights, and bellows (cuckoo whistles) are right for them.

In this post I calculate the run time (1 day vs. 8 day) of a cuckoo movement I recently bought, and the Links Per Foot of the chain it uses. These two numbers tell me what parts to buy to make a clock case for this movement.

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Calculating a clock’s Ideal Pendulum Period, The Sequel

In an earlier post I calculated the ideal pendulum period for the Korean clock by counting its wheels’ teeth (outer teeth) and pinions (inner teeth). This post is an update based on the errors I made while attempting to do the same for my second clock: the Ansonia kitchen clock.

What follows is a more detailed “how to” for calculating the pendulum period based on gear ratios.

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Dog Weight Scale Part 7: Choosing Matching Resistors

In my previous post, I worked through the calculations of weight and center of gravity when using four Load Cell Amplifiers instead of one.  In this post, I build the circuit for the first of the four Load Sensor / Load Cell Amplifier combinations I’ll be using.

The Sparkfun Load Cell Amplifier is designed to connect a Load Cell to an Arduino.  A Load Cell contains a full (4 resistor) Wheatstone Bridge, but a Load Sensor contains only half of a Wheatstone bridge.  To connect a Load Sensor to a Load Cell Amplifier, I need to add two resistors: R3 and R4 in the following diagram.  The dotted box represents the Load Sensor. The triangle in the middle of the diagram represents the Load Cell Amplifier.  As the weight on the Load Sensor increases, R1 decreases, which causes the voltage V1 to increase, causing the digitized amplifier output to increase.

Continue reading Dog Weight Scale Part 7: Choosing Matching Resistors

Dog Weight Scale part 6: Calculating the Dog’s Weight and Position

In my previous post I found the center of gravity of the top plywood circle of the Dog Bed Weight Scale. This post goes through the math of calculating the weight W on the scale and the position {X, Y} of that weight’s center of gravity.  That is, how much does our dog PIppa weigh when resting on the bed, and what is her position on the bed?

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Dog Weight Scale Part 5: Center of Gravity and a mounting Fail

In my previous post I described how to calibrate a load sensor. This post shows how to measure center of gravity, and shows a failed attempt to mount the load sensors to the scale.

Now that I’m using 4 load cell amplifiers rather than 1, I can calibrate each load sensor separately.  This in turn will let the Arduino calculate Pippa’s real weight accurately regardless of what part of her bed/scale she’s lying on.

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Dog Weight Scale Part 4: Calibration and its difficulties

Calibrating the scale using exercise weights
Calibrating the scale using exercise weights

In my previous post I finished assembling the Dog Bed Weight Scale, at least enough to allow testing it. In this post, I relate how I calibrated and tested it.

Using the Bogde HX711 Load Cell Amplifier library and examples, and the Sparkfun HX711 Example Arduino Sketches, I quickly wrote a little Sketch to output the raw value from the scale (SCALE = 1.0 and OFFSET = 0L).  The library made talking to the HX711 trivial.

Continue reading Dog Weight Scale Part 4: Calibration and its difficulties