Opto Endstop v1.0

Opto End-Stop

Darwin's Cartesian axes all need a datum (also known as home position or end-stop) to reference their movements. At the start of each build each axis needs to back up until the datum point is reached. For Darwin, we use one opto-switch for each axis to define its position. This page tells you how to wire one up to a bracket used in Darwin's design (below).

Preparation

You will need to buy in some parts and make up a PCB...

Bill of materials

You will need *3* assemblies for Darwin.

Electrical:

Component	Value	Quantity per SA	Total Qty	Description	RS/Farnell#
R1	220 Ohms	1	3	Resistor
R2	10K Ohms	1	3	Resistor
H1	H21LOI	1	3	Optoswitch	Farnell 102-1134
K1	3 pin	1	3	PCB transition connector

Mechanical:

			Part type
*Sub-Assembly (S.A.)*	*S.A. qty*	*Part*	*Qty per S.A.*	*Total qty*	*Fastener*	*Rod/Studding*	*Other*	*RS/Farnell No.*	*Moulded*	*RP*
Opto end-stop	M3 x 15 cap	6
	M3 washer	6
	M3 nut	6
	M5 x 20 cap	3
	M5 washer	3
	M5 nut	3
	Optoswitch bracket	3			1

PCB manufacture

All the KiCad circuit and PCB files are in Subversion at svn/reprap/electronics/Opto_endstop

Export a PDF of the PCB component sides (because they are small, the layout included 6 copies - it's useful to have some spares in case you loose or crack any of the boards). Use the PDF to make your own PCBs.

Drill hole diameters as defined below:

Assembly

You'll need a soldering toolkit to do most of this. Read our Electronics Fabrication Guide if you're new.

Insert H1, R1 and R2 on the component side, and solder.

Flip over, trim, and insert K1 onto the copper side. You will need to slide the plastic housing up the connector to give you room to solder.

Bolt the PCB onto the bracket using the M3 caps, washers on the bracket side.

You can now clamp the assembly to a Ø 8 mm bar by passing the M5 cap through the end of the bracket.

-- Main.EdSells - 01 May 2007