Circuit calculations

Works like MATLAB or a Jupyter notebook. Time a power-on reset circuit, then pick a status LED's resistor and its power rating from stock parts.

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Basin Ridge EngineeringNot checked yet

QuickCruit Compute

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/projects/circuit_calcs

circuit_calcs
circuit_calcs.qclive

Type: Live script
Cells: 4
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Name	Value	Unit

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circuit_calcs.qclive

How this notebook works
Write a number with its unit straight after it: 1.62 kg, 66 mm, 9.81 m/s^2. The notebook checks units as it goes and converts for you, so v to km/h shows a speed in km/h, and adding metres to seconds stops with a message.
Lists look like [0, 0.1, 0.25] s, ranges like 0:0.01:2, and positions count from 1, so x[1] is the first value. A one-line function reads area(d) = pi * d^2 / 4. Loops read for k in 1:10 or while v >= 0 m/s, and close with end.
Ctrl or Cmd + Enter runs every cell, top to bottom, with shared variables.

[1]

# Power-on reset: the line stays low until C1 charges through R1
Vs = 5 V
R1 = 18 kohm
C1 = 100 uF
t1 = 2.7 s                                                          # when the controller first reads the line
V_th = 3.8 V                                                        # the controller reads high from here up

# Status LED on the 12 V rail
V_rail = 12 V
Vf = 2 V                                                            # red LED forward voltage
I_led = 20 mA                                                       # target current
E12 = [1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2]  # times a power of ten, in ohm
ratings = [0.125, 0.25, 0.5, 1, 2] W                                # resistor power ratings in stock

# Power-on reset: the line stays low until C1 charges through R1
Vs = 5 V
R1 = 18 kohm
C1 = 100 uF
t1 = 2.7 s                                                          # when the controller first reads the line
V_th = 3.8 V                                                        # the controller reads high from here up

# Status LED on the 12 V rail
V_rail = 12 V
Vf = 2 V                                                            # red LED forward voltage
I_led = 20 mA                                                       # target current
E12 = [1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2]  # times a power of ten, in ohm
ratings = [0.125, 0.25, 0.5, 1, 2] W                                # resistor power ratings in stock

Your answers
Store each in the name the task asks for: tau, v_t, t_th, R_led, P_R and P_rating, and plot the charging curve. Add as many cells as you like.
[2]
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# Your work starts here

 
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# Your work starts here Tab indents. To move focus out of the cell, press Escape, then Tab.

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Run the script, or type a command after the prompt. It sees the script's variables.

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SI units

Two open items on the controller board before it goes to layout. Values are in the first code cell.

Reset: R1 and C1 hold the reset line low while the 5 V supply settles. I need four things: the time constant, the voltage at t1 when the controller first reads the line, the time the line crosses 3.8 V and reads high, and a plot of the charging curve for the design review.

LED: the red status LED on the 12 V rail drops 2 V and should run at 20 mA. Pick its series resistor from our E12 stock, then tell me how much power it burns and which rating to order.

Use the names from the notes, so the answers drop straight into the review.

Basin Ridge Engineering is a made-up company. A practice scenario, built for you.

The time constant of R1 and C1, in tau (s)
The capacitor's voltage at t1, in v_t (V)
When the reset line first reads high, at V_th, in t_th (s)
Plot the charging curve from 0 to about 5 tau
The LED's resistor, the next E12 value up from the exact one, in R_led (ohm)
The resistor's power in P_R (W), and the smallest stock rating at least twice that, in P_rating (W)

Checking runs the whole notebook first, then reads your named answers. Write units in and the notebook keeps them straight.

# Power-on reset: the line stays low until C1 charges through R1 Vs = 5 V R1 = 18 kohm C1 = 100 uF t1 = 2.7 s # when the controller first reads the line V_th = 3.8 V # the controller reads high from here up # Status LED on the 12 V rail V_rail = 12 V Vf = 2 V # red LED forward voltage I_led = 20 mA # target current E12 = [1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2] # times a power of ten, in ohm ratings = [0.125, 0.25, 0.5, 1, 2] W # resistor power ratings in stock

Circuit calculations

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