Blue Box Plans

by Ford Prefect

Readers:  We don't know if these Blue Box plans actually WORK, but we'd love to find out.  Please let us know and feel free to send along any other plans that you'd like to see spread among the populace.

Parts (A) +10 Volt (B) ICL8038 IC (C) 0.01 µF Mylar Cap (D) 82 kΩ Resistor (E) 100 kΩ Resistor (F) LM741 Op-Amp (G) 8Ω Speaker (H) 10 µF Capacitor (Non-Polarized) (/) SPST Momentary Normally-Open (NO) (↓) 1N914 Diode (I) Two 9V Batteries in Series (J) LM317T (K) 0.01 µF Capacitor (L) 470Ω Resistor (M) 3.3 kΩ Resistor

Parts Description (A) Connect the output from the power supply here. (B) Intersil ICL8038 Waveform Generator (C) 0.01 µF Mylar Capacitor (D) 82 kΩ Resistor (You will have to use two or more in series, resistance is additive in series) (E) 100 kΩ Resistor (5% is the best) (F) LM741 Op-Amp (G) 8Ω Speaker (H) (H) 10 µF Capacitor (Non-Polarized) (I) Two 9V Batteries in Series (J) LM317T Voltage Regulator (K) 0.01 µF Capacitor (L) 470Ω Resistor (M) 3.3 kΩ Resistor (/) Single-Pole Single-Throw Momentary-Contact Normally-Open Push-Button Switch (↓) 1N914 Diode RadioShack Part Numbers (B) 276-2334 (C) 272-1065 (E) 271-1347 (F) 276-007 (H) 272-1065 (J) 276-1778 (K) 272-131 (L) 271-019 (M) 272-028 (/) 275-1547 (↓) 276-1122

The spot on the diagram that has 700, 900, etc. should be filled in with a 25 kΩ multi-turn potentiometer (variable resistor).  The 15-turn pot from RadioShack (271-340) will work if a 1/4 watt, 5% 5 kΩ resistor is put in series.

The easiest way to tune the box is to play both it and a sample of the true sound together, the adjust the box until only one note can be heard.

As inaccurate as this sounds, this is more than accurate enough for the fone company.

The Apple with an Apple-CAT modem, the Atari, the Commodore, and the Texas Instruments can all generate the needed tones.

These plans are based on a set of plans I received two years ago.  They were almost illegible and the power supply included outdated parts.  The total cost is slightly above $50 but when properly assembled it will work perfectly.  (These plans have been field tested!)