LiniStepper v1. Microstepping Stepper Motor Driver Kit

How to build it! Assembly Instructions for the Original, Version 1 Kit. (Version 2 instructions are also available)
You need the usual small electrical tools and soldering iron with FINE tip, preferably temperature controlled. Although assembly is very simple and clearly laid out, it is expected that you have good soldering skills and some experience with closely packed circuit boards.

* HEATSINK! Cut and drill the alloy heatsink bracket or drill and tap the CPU fan
Please note that this is the heatsink bracket and is not a heatsink itself. A (much) larger heatsink should be clamped to the bracket. One advantage of using a CPU fan is that it can be directly mounted..

CAUTION: The Linistepper requires suitable, large heatsinking. Such as standard chunky aluminum/alloy heatsinks with fins. For additional heat dissipation use a bigger heatsink with extra fins, or a small computer fan to remove the excess heat. (steel is not a suitable heatsink)

Bracket Option (for the CPU fan, skip this section)

Use 25mm x 25mm x 3mm alloy angle, available at any hardware store. US size is 1" x 1" x 1/8". You need 100mm (4") length for larger motors like 1A and above, but can use a shorter piece (like the same width of the board) for smaller motors. See the picture for the 100mm example. Thanks to George Richards for sending along his PDF bracket cutting guide

Drill 4 holes to suit the 4 PCB holes, use the PCB as a template held against the bracket or CPU fan heatsink and use a ballpoint pen to mark the holes. See the picture for the positioning of the bracket. Drill the 4 holes 3mm or 1/8 inch diameter.

Drill 2 or 3 more holes on the other wall of the angle bracket which allow it to be bolted to the heatsink. Small motors may not need the additional heatsink, the bracket might be enough once mounted in a metal box etc.

With a 1A motor you need a big heatsink, about 1.5'C/watt as a minimum size, (that is about 400g weight (a pound) of alloy) It will be cheaper to use a smaller heatsink and a cheap computer fan (fans available for under $2 these days). Remember to heat-test your heatsink for at least 1/2 hour at full power to make sure that the 4 main transistors don't get over 25'C rise (not over 45'C total).

CPU Fan Option

If you use a CPU heatsink/fan, you can mount the TIP 122 power transistor's to the face that would normally press against the CPU, and mount the bottom edge of the heatsink fins to the top of the Lini PCB where the transistors would normally be bolted (see the picture below).

Check the length of the leads to see where the holes in the CPU fan heatsink face should be placed.The best location is just a bit above center.

Use the PCB as a guide to mark the locations for the power transistors mounting holes, then center punch and drill.
See: http://www.piclist.com/techref/taps.htm#drillcalc for information on tap and drill sizes.

Again, using the PCB as a guide, mark 2 or 4 holes on the bottom fins of the CPU fan heatsink to use in mounting the PCB. Drill through several fins, then carefully tap through those fins to provide threads for your mounting bolts to grip into. Go deeper than you think you need to because each fin only provides a few threads to hold the bolt.

* Inspect the board Check the board is ok, check for broken tracks, filled solder holes etc.

* Check all the bits are there Check through the parts and compare to the parts list to see if there are parts missing, damaged or exchanged for different types. If you are building a special version of the board, like a high current one that needs different resistors, make sure you have the extra parts before you start.

Part	Package	Photo	Description
Q1-4	TIP122		Power transistors
Q5-8	TO-92		Switching Transistors
IC1	DIP 18		PIC Microcontroller
			Socket
R1-2	3 Watt		Power Resistors
R3-6	not supplied		used to tune for higher power
R7-31	1/4 Watt		Resistors
C1	big radial		470uF Electrolytic Capacitor
C2,4	Disk		22pF Capacitors No longer needed or supplied
C3	blob		10 to 22uF Tantalum Electrolytic Capacitor
C5,6	disk/blobs		2.2 to 4.7uF Electrolytic Capacitors
D1-6	axial glass		1N4148 Diodes
XT1	blue disk		ceramic resonator Now a three lead resonator (eliminates C2 and C4)
			Misc: Nuts, bolts, washers, mica insulators, heatsink grease pin headers, connectors, etc...

* Solder the flat parts first.
This means resistors and diodes mainly.

Resistors
The resistors come in two types, 4 band and 5 bands, referring to the number of colors on the bands. The kit may come with 5 band metal film resistors, 1% tolerance. Make sure you get the resistor values right BEFORE soldering them in!

Do them in blocks of 4 or 5, the way the board is layed out. Insert the 4 resistors, put the colours the same way around making them easier to read, and splay the legs a bit to hold them in. Then invert the board and solder them in, finishing by removing the excess legs with fine point wire clippers.

Notice below the 6 "microstep tuning" resistors are mounted on a bit of an angle to make them fit.

Diodes
There are 6 diodes, WATCH OUT the diodes are NOT all the same way around, they are layed out like in the circuit diagram:

--   |--
--   |--
--|   --

--   |--
--   |--
--|   --

The diodes MUST be the correct way around.

PIC Chip
First solder in the socket, making sure the notch end of the socket goes toward the OUTSIDE of the board. The socket and the PIC must be the correct way around!

Don't insert the PIC into the socket until the board is complete.

Oscillator/PIC parts
The PIC has a 16 MHz ceramic resonator which is now supplied as a three lead unit that does not require the 2 small 22pF caps C2 and C4. Insert the the resonator, keeping the writing on the parts pointed out so you can read it.

Capacitors

Insert the tantalum cap C3 next to the PIC. It MUST be in the correct way around, the + lead (which is the longer lead; the mark is hard to read on the cap) goes toward the board edge.

Other caps
The two small caps (C5,C6) and large electro cap (C1) can be inserted next. All these caps MUST be inserted the correct way around! In each case the + of the cap goes towards the big transistors.

Connector pins
Make sure these are cut into 2 strips of 7 pins, and solder in as shown in the picture above. These have a low melting point, and must be soldered QUICKLY with a clean soldering iron tip and fresh solder. It may help to clamp the pins with a metal clamp etc to keep them cool when soldering.

Small transistors
The 4 small transistors Q5,6,7,8 are inserted as shown on the board itself. Don't push them all the way down, leave about 4mm of legs above the board. Solder each one by one leg only to start with, and then you can straighten them and make them look neat before soldering the other legs.

* The big transistors need special attention
Once the flat parts are all done you can do the fiddly stuff, of which the most fiddly are the power transistors.

* mount the heatsink bracket, or the CPU fan, to the board with 2 bolts. For the bracket, use the outside two, for the fan, the inside two. The bracket or fan goes on TOP of the board.

* once the bracket or fan is secured, it's time for the 2 middle transistors to go in;

• tiny blob of heatsink grease on the bracket or fan where the transistor will go.
• cut the clear mica insulator to size, see picture

  

• place insulator on blob
• another blob on top of insulator
• For the bracket bend transistor legs NOT QUITE 90 DEGREES (see picture), for the fan, they remain unbent.

  

• place transistor in correct spot and add the inner washer and bolt, and for the bracket add nut on the other side (see picture)
• solder legs before final tighten of the bolt

* Do the middle 2 transistors first, the outer 2 after.

IMPORTANT!
After insterting all 4 of the power transistors make sure the clear mica washers and cream insulator washers are in correctly. This can be checked by testing that the metal tag of the transistors ARE NOT CONNNECTED to the heatsink (use an ohm meter).

Next are the big 3W resistors
mount these about 6mm above the board to keep them cooler, and also this provides a place to attach the CRO leads if you wish to view the current waveform.

IMPORTANT!
You must add two 470 ohm resistors on the bottom of the board and these must be added exactly as shown in this photo (bend and cut the leads to suit and then solder);

Finally you should have a completed board!
Check the board carefully with the photos and board layout diagram. Be sure to check the following:

• capacitors are the correct way around
• right resistors in the right places
• power transistors NOT shorted to heatsink!!
• PIC chip inserted with "notch" toward the board edge

Hopefully it will look something like this:

Now you can move on to using the board and keeping it cool. at http://www.piclist.com/io/stepper/linistep/lini_use

We very much recommend using our Linistepper "4 AXIS / Mode / 555 / PWR" kit to drive the Linistepper.

-end

Questions:

• andreas@kaenner.de asks: " what are the two 470 Ohm resistors for? I can't find them in the circuit diagram." They are added to the bottom of the board, as shown in the picture above (second to last photo) This was a modification that was added to improve function after the PCB's where already made.
• Dale askes: "James, I'm stumped. Resistors R18/19 thru R28/29 don't seem to match the circuit diagram with the the pictures on the web site. I have enough parts to populate the board but the resistors would have to be vertical, the picture looks like only half of the resistors are used??? Please advise."
   
  The extra holes and resistors shown on the circuit are actually a prototyping area, as using two resistors lets you fine tune the microstep currents. For the standard currents of 1200 steps I was able to choose resistor values using 1% resistors that give good current settings.  But this is a design that can be used for more than one setup, and hence the extra holes let you tune microstep currents by putting 2 resistors in series to get in-between resistor values.
   
  There are also extra holes for the large resistors, to allow the use of extra power resistors in parallel. This enables tuning the MAIN current, ie the 100% value that all the microstep currents are based upon.
   
  Thank you for pointing that out... It does need to be made a bit clearer. In the instructions that Roman wrote, the board layout picture was not included, only the actual photos of the board. At the suggestion of another person, I added the board layout picture, which had not been updated since the change. I have now updated the board layout picture that should correct the confusion, but your question and this answer should be of use as well.
   
  Thanks again and sorry for the confusion.
   
• bcoenen@kc.rr.com asks: " Do you sell just the printed circuit board, and how much?"

  After thinking about your question for a while, we decided to make a set of 3 boards available for $35.00. These are VERY well made boards and are certainly worth the price IF you have a well stocked inventory of parts in your scrap box to populate them. With the kit of parts only $25 each quantity 3, I don't think you will ever find the parts for less from another vendor.

Questions: