PCB Board 3

PCB Board Number 3

Having completed two boards previously (Board 1 and Board 2) I expected board 3 to be straightforward.

Up to a point this was true - the biggest problem was finding exactly the required component in the available libraries.

1. Previously used components.

I did not expect to have problems with components already used in projects 1 and 2. The problems were different variants from different manufacturers. Even selecting simple components like 2 pin screw connectors used in the previous boards was not entirely straight forward. One problem with the 2-pin screw connectors was the size of the hole. See appendix. My recommendation is for every project to generate a BOM (Bill of Materials). From menu select Fabrication -->BOM.

2. "New" components.

The above schematic is for a project based on an ESP8266 that will:

(i) Detect the location of a model train using sensors S0 to S7. This information will be the inputs to a parallel to serial convertor (74HC165) to become the serial input to the ESP8266 (Wemos).

(ii) The train status will be used to set up 4 sets of signals (Red,Amber,Green) to control following trains. Since the ESP8266 has limited pins a serial to parallel convertor (74HC164) is used to generate the Red and Green. The 74HC02 NOR gate will generate the Amber signal.

(iii) The ESP8266 will also act as a WiFi hot point that can transmit the train status to a smartphone.

The Wemos D1 was available as a user contributed package. For the 74HC00 series devices there were many variants available however most of these were for surface mounted devices so once again once you have found the device you want document it for future reference. EasyEDA does have a "My Favorites" library that might be worth investigating.

The final PCB is shown. Initially it was found too difficult to wire the tracks with the two DIL packages axially. It was much easirer when they were both parallel as shown.

3. "Unavailable" components.

For any components that are not available it will be necessary to generate a user defined symbol and footprint. For a first project this should take between 20 and 30 minutes. The process is discussed in a separate page NewComponent

Appendix.

Photo of completed board shows 2-pin screw connectors at all angles due to holes being too large. The hole diameter needed to be adjusted.