This little circuit makes it possible to send data from the Embedded Communications Connector over a RS485 link. It only uses one small IC, a led, a few passive components and two connectors. We already used this particular IC in our series ‘Here comes the Bus!’ (110258, USB/RS485 Converter).

 

To keep this module as small as possible most components are SMD and placed on the bottom side. Placed on the top side are two connectors, a jumper and a led for power indication. By using SMDs on the bottom side the two connectors can be placed very close together. Building it by hand shouldn’t prove to be difficult.

 

Bill of materials

 

Resistor (SMD, 0805, 125 mW)

R1,R2 = 10 kΩ, 5 %

R3 = 120 Ω, 5 %

R4 = 1.5 kΩ, 5 %

 

Capacitor (SMD 0805)

C1 = 1 µF, 10 V, 10 %, X7R

 

Semiconductor

D1 = led green 3 mm (low current), through hole

IC1 = LT1785CS8#PBF (SO-8)

 

Other

K1 = 10way pin header, 2x5, lead spacing 2.54 mm

K2 = 3way terminal block, lead spacing 5.08 mm

JP1 = 2way pin header, lead spacing 2.54 mm + jumper

 

Misc.

PCB = 130155-1 v1.2