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PB Machine
Electronics + SMT Soldering
Development of a compact analog circuit combining a custom PCB, surface-mount soldering, through-hole assembly, and an LM3914-driven LED display.
Type
Analog Electronics
Driver
LM3914
Input
Adafruit Mic
Fabrication
SMT + THT Soldering
Development
PCB Assembly
Analog Circuits
Project Context
The PB Machine was developed to learn SMT soldering while creating a small analog circuit. The project was completed in two parts: assembly of the PB Machine PCB and development of the supporting LM3914 circuit.
Reference
01
The project combines surface-mount PCB assembly with an analog LM3914 circuit that senses an analog voltage level and drives a sequence of LEDs.
The PB Machine itself consists of the PCB, 3mm barrel jack, 103 SMT resistor, SMT green LED, and GPIO pin headers.
The supporting circuit uses an LM3914, microphone with amplifier, and ten individual LEDs to create the analog display.
02
The PCB provided a platform for developing and practicing both surface-mount and through-hole soldering.
Surface-mount assembly began with the SMT green LED. Solder paste was applied to the PCB using a toothpick and the components were positioned using tweezers.
The hot air station was heated to 300° and moved in a circular motion to melt the solder paste and solder the components to the PCB.
After the surface-mount components were complete, the through-hole parts were soldered into place to finish the PB Machine assembly.
PB Machine PCB
SMT and through-hole PCB assembly
PB Machine
03
The surface-mount components were assembled using solder paste, tweezers, and a hot air station.
01
Solder Paste
Solder paste was applied directly to the PCB using a toothpick.
02
Placement
Surface-mount components were positioned on the board using tweezers.
03
Hot Air
The hot air station was set to 300° and used in a circular motion to melt the solder paste.
04
The analog circuit is built around the LM3914 and converts an analog voltage level into a sequence of LED outputs.
The LM3914 senses analog voltage levels and drives up to ten LEDs, creating a series of linear outputs. The IC has 18 pins and can switch between bar and dot display modes using pin 9.
The report lists an operating voltage of 3-35 volts. Inside the LM3914 are ten comparators and a resistor. As the input voltage increases, additional comparators turn on.
05
The LM3914 provides two different methods of displaying the incoming analog level.
Mode 01
Dot
In dot mode, only one LED is high while the remaining LEDs stay low.
Mode 02
Bar
In bar mode, every LED up to the highest active level is turned on.
06
The LM3914 uses a series of comparators to determine which LED outputs are active.
A comparator compares two voltages or currents and outputs a digital signal indicating which is larger. It has two input terminals, V+ and V-, and one digital output, Vo.
In the LM3914, ten comparators are arranged in parallel with 1kΩ resistors separating them.
07
Parts Table
Qty.
9V DC Alkaline Battery
1
3mm Barrel Jack
1
LM3914 IC
1
1.5mm Green LED
6
1.5mm Yellow LED
2
1.5mm Red LED
2
2.2 kΩ Fixed Resistor
1
3.3 kΩ Fixed Resistor
1
Adafruit Mic with Amplifier
1
LM7805 5V Voltage Regulator
1
Full Breadboard
1
103 SMT Resistor
1
SMT Green LED
1
PB Machine PCB
1
Male GPIO Pin Headers
6
Wires
Assorted
08
The completed project combines the surface-mount PB Machine PCB with an analog LM3914 circuit and microphone input.
PB Machine Close-Up
Completed PB Machine
VU Meter Circuit
LM3914 circuit assembly