Isolated RS485 HAT

With the invent of the model B+ and Raspberry Pi Rev 2 HAT’s have become the common format for add on boards. So this gave me the perfect excuse to update my isolated RS485 board and add a couple of extra features like DIP switches to replace the jumpers and transmit and receive LED’s. The picture below shows the HAT board connected to a raspberry pi model B+.

Rs485 hat
Isolated RS485 HAT

 Technically it isn’t a HAT because there is no EEPROM fitted but it is in the HAT format.

The Schematic below shows the revised design with the jumpers replaced with DIP switches and the TX and RX pins buffered to the LED’s

 

 

Isolated RS485 Raspberry Pi Hat
Isolated RS485 Raspberry Pi Hat

 

The BOM for the project is

9 Resistors

Quantity:                  References                Value
2                                 R1, R5                         120
2                                 R2, R4                         560
1                                 R3                               3.9k
2                                 R6, R7                         10k
2                                 R8, R9                         270

8 Capacitors

Quantity:                  References                Value
2                                 C1, C6                         10n
2                                 C2, C3                         10uF
2                                 C4, C7                         10u
2                                 C5, C8                         100n

4 Integrated Circuits

Quantity:                 References                   Value
1                                 U1                                  ADM2687E
1                                 U2                                  ADP122
1                                 U3                                  555
1                                 U4                                  SN74LVC2G17

3 Diodes

Quantity:                 References                     Value
1                                 D1                                     1N4148
2                                 D2, D3                              LED

4 Miscellaneous

Quantity:                  References                       Value
1                                  DSW1                                 DIPSW_4
1                                  DSW2                                 DIPSW_5
1                                  J1                                         TBLOCK-I5
1                                  J2                                        CONN-DIL40