Dennis Brown: Top side bed switches: Assembling the switches - psmay/mpmd-notes GitHub Wiki

Source

The original version of this came from https://www.facebook.com/groups/mpminideltaowners/permalink/2471312799550858/, written by Dennis Brown, as it was 2021-04-01. Refer to that post for updated information and comments. Some reformatting has been applied (its correctness is not guaranteed).

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How to make the switches for the upgraded MPMD bed switches seen in this post:

Dennis Brown: Top side bed switches

A) 3D Print the switch circuit board holder on a working printer.

You may have to clean out some strings in the slot. The slot is designed so that it is smaller at the top than the bottom. It also has a bit of give to it. This is so that the wires that go into this strain relief slot will stay put. The top wires will hold the lower ones in place, so don't go crazy widening out the slot when it is cleaned out.

The OpenSCAD file for this object is here:

MPMD_BedSwitchBox.scad (Source: https://www.facebook.com/groups/mpminideltaowners/permalink/2471048596243945/)

The .stl file is here:

MPMD_BedSwitchBox.stl (Source: https://www.facebook.com/groups/mpminideltaowners/permalink/2471036529578485/)

B) Assemble the inverter circuit board.

Unless you are an electronics DIYer, I highly recommend getting an already kitted up or assembled set from: to be determined. This will save you a lot of time and money.

If you are or want to become handy with electrical projects, I list the parts and amazon prime sources that I have used or equivalents I could find. You may already have some or most of these parts or know of other places to get them in smaller quantities at a better price.

PARTS list and sources:

(1) 0.3" x 0.7" 0.1" perforated proto board

I built the circuit board on a 0.3" x 0.7" perforated proto board. It has a plated through hole and pad on a 0.1" x 0.1" grid. This makes it easy to cut to size and solder through hole parts. I cut mine out of a larger board with some metal shears. I also filed the edges a bit, since it is a fiberglass board. Amazon carries this type of proto board, though you will end up with a lot extra for future projects. Here is a nice assortment for $9. There are a lot of other assortments available:

https://www.amazon.com/Paxcoo-Double-Sided-Board-Prototype/dp/B01M7R5YIB/

(1) 2N3904 Transistor. I happened to have a few in a drawer already. These are a staple for DIYers. Amazon sells them in 5 lots for $4 or 100 lots for about $8:

https://www.amazon.com/NTE-Electronics-2N3904-Transistor-Amplifier/dp/B008UFYCZG/

But for a few bucks more you can get 25 each of 10 different types of DIY transistors for $9:

https://www.amazon.com/Eowpower-250PCS-Values-Transistors-Assortment/dp/B071LNGS94/

(1) 150K Ohm 1% tolerance thin film resistor. You can not substitute another value for this. It is calculated based on the input pull up resistor internal to the processor chip and the 2N3904 gain. Hard to buy just one. Amazon has 50 packs for $4:

https://www.amazon.com/50-Resistors-150K-Ohms-OHM/dp/B00KVGKQHA/

I have a resistor assortment kit with all the common values for my DIY projects. Amazon has assortments, but be careful, because many of the assortments do not include the 150K value. Here are some that do for about $12. The last one on this list looks like it is nicely sorted:

https://www.amazon.com/Anezus-Resistor-Ohm-10M-Resistors-Assortment/dp/B07GDLDF1X/

https://www.amazon.com/Top-cofrLD-Resistors-1640pcs-resistors-Assortment/dp/B00WE1FQ8Y/

https://www.amazon.com/Ltvystore-1500pcs-Values-ohm-Assortment/dp/B01N0H84HS/

https://www.amazon.com/Precision-Electronic-Assortment-1ohm-1Mohm-Geekstory/dp/B079FP5WD9/

(2') #22 AWG solid copper hookup wire. I used solid wire instead of stranded, because it is stiff and will stay put when you bend it the way you want it to go. It is also more robust at the solder connections. If you don't already have this, you can get one small roll for about $6.50:

https://www.amazon.com/NTE-Electronics-WHS22-06-25-Solid-Length/dp/B008CF7GP2/

I bought 5 rolls of 25' each of 5 different colors, to also use for other breadboard projects for $16:

https://www.amazon.com/dp/B077HRKYB1/

(3) 4-40 x 1/4" Flathead Socket screws. These are the adjustment screws for bed leveling (buy a few extra):

https://www.boltdepot.com/Product-Details.aspx?product=5543

(3) 4-40 x 3/8" Flathead Socket screws. That are a longer set in case the bed is way out of level and needs a longer screw (buy a few extra):

https://www.boltdepot.com/Product-Details.aspx?product=4442

(3) 16-22 AWG insulated #10 Ring solderless connector. You usually have to buy a pack of these. Amazon has a 100 pack for $9.50:

https://www.amazon.com/Vinyl-Insulated-Ring-Connector-22-18/dp/B07796C4ZV/

You can also find assortments to put your money to better use. This assortment would have both the previous and next connector covered with 5 of each for $15:

https://www.amazon.com/dp/B07F1TL9Y7/

(3) 16-22 AWG Insulated 0.25" Spade Female solderless connector. This is an automotive or marine version that is fully insulated over the whole contact area. This is needed to make sure the bare metal does not bump into the edge of the aluminum bed and short to it. Amazon has a 100 pack for $7:

https://www.amazon.com/gp/product/B01823DKVM/

You could also get the ones without insulation and put heat shrink tube around it.

(2) 3 Pin Female JST 1.25mm Connector with 150mm wires. These are the connectors that fit into the switch connectors on the motion controller board. 150mm of wire is enough to reach the closest switch or to the connector on the controller. Technically only one is needed to plug in to the controller board. However, leaving the existing bed switches connected is an added safety factor in case the new switch circuit fails for any reason. Amazon has 20 pieces for $8:

https://www.amazon.com/gp/product/B075YFMXNP/

(3) 0.25" x 1.25" x 0.025" Brass strip. You can get brass in 0.25" x 12" long strips and only have to cut to length. Amazon has a single pack for $7:

https://www.amazon.com/gp/product/B00FZS2GGI/

(3) 1" long pieces of high temperature transfer adhesive. 3M 468MP is the type of adhesive that is usually used to apply bed things to 3D printer heated beds. Amazon has 3/8" x 5 yd rolls of this tape available for $5:

https://www.amazon.com/3M-8-5-468MP-Adhesive-Transfer-Length/dp/B06Y34587N/

ASSEMBLY Instructions for the inverter board:

Start by soldering the wires from the JST 3 pin connectors onto the PCB. Only two wires on each connector are used. In the wire set I linked to, it is the yellow wire that is not used. Solder the two red wires in the same hole as shown in the underside photo, then the two black wires. Do not overheat the connection or the insulation will melt. The yellow wires can be removed. If you put some pointed tweezers under and lift the plastic catch, the wire and contact will slide right out.
Next insert the 2N3904 transistor into the 3 holes as shown in the underside photo. The red outlines show where the flat is on the package. The leads do not match the holes directly, so they will have to be gently pressed and wiggled to get it to go down most of the way. The transistor will stand off the board about the height of the resistor body diameter. Bend the leads over slightly so it does not fall back out of the holes.
The 150K Ohm resistor goes in next. Bend the leads of the resistor 90 degreed down as close to the end of the body as you can without putting a sharp kink in the leads. Insert the leads in the holes shown. It will have togo flat against the board tucked under the edge of the transistor. Bend the legs apart so it does not fall out. The leads are clipped somewhat close to the board as shown.
Push the transistor in tight again and bend the leads over flat against the board like shown. Clip the ends of the leads as shown.
Solder all 5 spots where a lead is going through the board, but just enough to get them tacked into place.
Cut a 1.5" length of 22 AWG hookup wire and strip 1/8" off one end. This one goes into the hole next to the resistor.
Cut a 4.5" length of 22 AWG hookup wire and strip 3/8" off one end. This wire goes into the other hole and the lead is bent over to touch the transistor lead that is bent away from it. Clip it to just touch the transistor pad.
Solder all three part runs together quickly.
Make a sharp bend with the long wire around the circuit board to the back side as shown.
Clip any excess lead lengths from the back of the board.
Slide the circuit board into the printed holder part all the way in.
Carefully route the red, then the black connector wires through the wire strain relief slot. Push them down from the top of the slot.
Clip the short wire 1" long from the plastic part.
Clip the long wire 3.75" long from the other side of the plastic part.
Strip 1/4" from the end of each of the two wires.

C) Assemble the bed switch wire connectors.

Cut two lengths of 22 AWG 4.75" long. Strip 1/4" from all 4 ends.
Crimp a #10 ring terminal to one end of each wire, and to the short wire of the inverter board assembly.
Crimp a spade receptacle terminal to the other end of the wires and the long wire of the inverter board assembly.

D) Make and assemble the bed plate contacts.

File any rough edges off the 3 cut to length brass strips. Make sure they are absolutely flat. Tweak them with some smooth face pliers if needed to flatten them.
Push the strips (cut side first), into the spade receptacle connector. If for some reason, the contact is not tight, then crimp the contact a bit and try again.
Clean the brass with 91% Alcohol.
Attach the 3M 468MP transfer adhesive onto one exposed side of the 3 brass contacts. Cut around it with scissors or razor knife, but do not remove the paper liner yet. Pay attention to which side the adhesive goes on in the photos.

THE SWITCH SUB-ASSEMBLIES ARE NOW COMPLETE