UPC EETAC Bachelor's Degree in Telecommunications Systems and in Network Engineering EEL

 

Soldering and prototyping

P1

Lab 1.0

Logic probe for experimentation

Prototype specifications Planning Development Test & measurements Lab

Laboratory prototyping is a fundamental phase in circuit design. To practise with lab tools and develop some initial skills, we will solder components to a printed circuit board (PCB). Let us conceive a simple instrument: a logic probe, to visualise logic values and detect digital signals.

- High level in a red LED. Low level in a green LED.

- Tri-state or floating voltage in a yellow LED.

- Oscillating digital signals in a white LED.

- CMOS and TTL compatible.

 

Fig. 1. Logic probe.

 

Prototype specifications Planning Development Test & measurements Lab

Planning steps are required for both, designing the logic probe and developing the prototype.

Using a versatile analogue comparator like the LM339 that can work up to 30 V, allows the compatibility with CMOS and TTL logic families.

 

Logic probe circuit

Step #1: detecting logic '1' and '0'

 

Step #2: detecting floating signals or tri-state wires

 

Step #3: detecting oscillating digital waveforms

 

 

Printed circuit board (PCB)

 

 

Prototype specifications Planning Development Test & measurements Lab

 

Circuit capture in Proteus

 

This is the "Logic_probe_prot_v1.pdsprj".

Complete circuit

Fig. 5. Complete circuit captured in Proteus.

 

Printed circuit board (PCB)

As indicated

The add-on PCB design starts capturing the schematic in KiCad as shown in Fig. 5.

 

Fig. 5. Schematic captured in KiCad.

The PCB component placement is shown in Fig. 6.

Silkscreen

Fig. 6. PCB layout silkscreen that shows component placement and references.

Finally, a 3D view shows the real dimensions and how the PCB will look like once soldered.

 

Fig. 7. PCB 3D representation.

Additionally, we can set several parameters for easy routing, manufacturing and soldering, such clearance between components and tracks (0.3 mm), signal (0.5 mm) and power (1 mm) track widths.

Fig. 9 shows the process of placing and soldering components on the board's prototype once manufactured using our lab machines. At this stage, we have to verify that the board works as expected or, if it is the case, make the necessary adjustments.

Fig. 9. The idea of placing and soldering components on the PCB.

 Once this final revision step is completed, the PCB is ready for manufacturing as shown in Fig. 10.

Fig. 10. The final manufactured board with the silkscreen layer labels printed.

Board's picture in Fig. 11 shows the current prototype board with all the soldered components.

 

Fig. 11. The idea of placing and soldering components on the PCB. The final manufactured board with the silkscreen layer labels printed.

 

Prototype specifications Planning Development Test & measurements Lab

Circuit simulation

Validating the circuit in Proteus

 (reverse test & measurement for LAB)

 

 

 

 

Prototype specifications Planning Development Test & measurements Lab

 

 

C) Run the circuit and test operations

 

D) Power consumption

 

 

Annexes