Yeah a straight rod, while simpler to build mechanically, adds a lot of complications to driving the build - like you say John P, drive speed is dependant on how far up the rod the top platform would be etc. The design I am opting for is much simpler in the long run and less error prone.

Ok I will go with a 1:1 ratio for the external gearing then (assuming I can get the necessary hardware and engineer it to purpose, but 1:1 should give me the best chance of doing so), meaning I will need the motor to run at exactly 64rpm for a shaft speed of 1rpm. Nice and simple... in theory

Good to know the heat sink set-up looks sound. Actually I meant to say that the amount of goop you get in the kit is really a tiny amount - I know you only need a little but I was really scraping the last of it up, and ended up rubbing the little pack it comes in over some of the surfaces to salvage every last bit. Not sure if I got an unusually small amount with mine.

I think I want to buy some more to top it up, as it is certainly not enough to form a small bead around the washers like in the build instructions. What sort of stuff can I use, is it the same thermal paste you buy for CPU application?

Ok I'll test the transistors are not connected to the heat sink tonight - so to do this ( newb instruction time ) I put one probe on the heat sink, and one on the metal part of one of the transistors, turn the MM to the lowest ohm setting (I dont think it has a beep setting) and if it is all good the it should read infinity?

Cheers

UPDATE: I just got around to testing for shorts, and all is good, no shorts on any of the transistors to the heat sink buffer plate. I also did the rest of the shorts tests on the build instructions (C3 and C1 caps) and they are sound too.

 

... Ok I will go with a 1:1 ratio for the external gearing then (assuming I can get the necessary hardware and engineer it to purpose, but 1:1 should give me the best chance of doing so), meaning I will need the motor to run at exactly 64rpm for a shaft speed of 1rpm. Nice and simple... in theory
...

1:1 gears also gives you a benefit you just need to find two identical gears.

As for "exactly 64 RPM" at the motor, that's a good starting point but it's possible your final mechanical build will not be a perfect distance from the pivot point to the centre of the rotating nut, so you might need to tweak that RPM a tiny bit.

Wood is not my ideal material either as it cracks and also swells and warps with moisture etc (and this will be used outdoors at night!). You can buy acrylic (perspex) in 1/2" thickness and it works fine with wood tools like holesaws etc. Just a thought.

... Good to know the heat sink set-up looks sound. Actually I meant to say that the amount of goop you get in the kit is really a tiny amount - I know you only need a little but I was really scraping the last of it up, and ended up rubbing the little pack it comes in over some of the surfaces to salvage every last bit. Not sure if I got an unusually small amount with mine.

I will definitely pass that info on to the kit guy, you may have just got one with a smaller blob of goop.

If you want you can use any normal "heatsink compound", that should be fine. However in your case it may not be worth the effort, the kit is specced for 1.5A drive and you are only running a very small motor at 100mA or so, so heatsinking is unlikely to be an issue in your build.

Dissipation when running at 130mA will be about 160mA per transistor pair, or only about 80mA average per transistor. With about 5v motor voltage and 1v on the sense resistors the power transistors will have an average 12v - 5v-1v ie 6v at 80mA each, a dissipation of 0.48 watts each. That is quite low really.

 

Ah good point about the wood warping, I had not considered that. Sealed plywood should hopefully have very little warping, but I will look into that and consider alternative materials if I think it is needed

Ok great, well I will forget about the goop for now and just see how hot it gets, then add some thermal paste if needed.

I have just received all the additional parts (5v voltage regulator, 47uf 16v capacitor, switches, resistor for led power switch) - could you advise ( in an amateur friendly fashion ) on how I need to connect them up to the PCB? I am unsure where the capacitor / voltage regulator will be mounted at the min as I am sure they will need to be mounted to something. I think for the min I will leave out the speed / direction switches and just hook up the power LED switch and the rest of it.

I also have the 8.2 ohm resistors for the linistepper - is there an easy way for me to identify which way to solder them on to the PCB? And do they go in the R1, R2 holes (wider apart ones) as opposed to R3, R5? The colour of the bands looks like grey, red, gold, gold.

Cheers

 

They are "82 gold" which means 82 and /10 or 8.2 ohms, all is good.

They go in any of thos holes, I would use the wider apart holes, R1 etc. (Multiple holes are provided in case people use multiple resistors in parallel.)

Re wiring;
Normally the 7805 is screwed to the side wall of your metal box. It does not need isnulating as it tag is GND, this just grounds your metal box.

Then the cap(s) are trimmed and soldered direct to it's legs. It's good to check the 7805 datasheet, but with the TO-220 pack the legs are (left to right); Vin, GND, Vout
if you have two caps put them both on the regulator, one on Vin to GND, one on Vout to GND. (The - stripe on the cap goes to GND).

Vin goes to the power switch. Vout is the +5v regulator output, that goes to the Lini +5v power input. Battery - is GND, connecting to the 7805 GND and Lini GND.

The power switch also goes to the M+ terminal on the Lini, and to the stepper motor common ( RED) wire. Good practice is to use RED for +, BLACK for GND, and another colour WHITE etc for other wires like control wires.

The other side of the power switch goes to the battery + terminal, so the power switch completely disconnects the battery + terminal from everything.

(This is sounding a bit complex but the wiring is really very simple. I'll draw up a rough diagram and scan it and post it here next time I'm on).

If I remember right, once 12v, 5v, and GND are connected (and the motor!) the Lini should run the motor (provided it has been programmed).

 

Yeah it does sound a bit complex Like you say I am sure it is not really, but it is a lot to take in from just text - a diagram would really help me visualise this so I would appreciate that a lot if you get a spare second. Also where in that does the 1k resistor go for the LED switch? The switch has 2 pins and also 2 LED pins at the bottom. In the listing it says "As the contacts of the LED are separate, the LED can be used for status indication etc"

I checked the datasheet for the 7805 and it is indeed as you listed

I don't think you clarified - does it matter which orientation I solder the two 8.2 ohm resistors on to the linistepper?

Here is the LED switch contacts and the 1k resistor:

Cheers

 

Resistor orientation does not matter. Personally I like to make them neat for easy reading of colour codes.

The two long skinny wires in the switch are the pins of the LED. The longer one is the ANODE (+ pin).

I have attached a rough (ahem) scribbled diagram for you. It should be easy enough to follow.

The three small switches near the Lini control SPEED, DIR, and RUN. If you have a main power switch you can just connect the RUN wire to ground. That will make it permanently RUN, then you have two switches for direction and speed.

I have shown how to put the caps close to the 7805 pin, soldered to its legs.

As for general wiring points that is up to you, normally I would use the GND wire of the 7805 as the main ground point and attach all black ground wires to that.

Also I forgot a couple of parts, an inline fuse holder would be good for safety on the main battery + wire, as that battery is capable of some violence if a wire comes loose and shorts out. A 1.5 amp fast blow fuse is fine.

And for precise timing your should have ordered the Lini with the 16MHz xtal option, as that gives the most exact timing and immunity to temperature variations. I'm sorry if I didn't mention that earlier! I don't do a lot of Linistepper tech support these days. Any 16MHz standard sized xtal will do, and you need two small 15pF or 22pF ceramic caps as well to go with the xtal.

For testing it will work fine with the 16MHz resonator you have, but the speed might be up to 200 PPM out (a fraction of a percent).

(edit) You also might want to get a 2x5 pin 0.1" header to plug into the 10 pin socket on the Lini, to allow easy removal of the Lini PCB.

Diagram is now fixed, see below

 

Woah, more parts to get!

Ok got a few questions concerning this diagram ( thanks very much for taking the time to do this by the way ) I have not used circuit diagrams before. Sorry that I need clarification on a lot of things, I hope you do not find it too frustrating.

1. I am going to leave out the 3 switches at the bottom for now. My mechanical design allows me to disengage the gears easily to reverse / reset. Like you said I won't need a run switch at all.
2. what do the black dot 3 way junctions in your diagram represent? Do I literally run a piece of wire off another one in the middle by cutting away the plastic coating? Or is it that there are actually 2 wires running together and this is where they run away from each other.
3. The LED is built into the main power switch, so does that affect the diagram / wiring?
4. At the bottom right there is a symbol with a few lines - I think this means ground? Does the fact that that symbol is there mean that I have to do something at this point? What is the difference between that and the GND symbol written like that?

Ok onto the additional parts, how do these guys look:

Fuse holder
http://www.maplin.co.uk/universal-in-line-fuseholder-20624

xtal - this says it has ±30ppm freq accuracy - is that any good?
http://www.ebay.co.uk/itm/120926165756?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

15pf or 22pf ceramic caps
http://www.maplin.co.uk/metallised-ceramic-platecapacitors-304

I have found some old gears in a meccano set which look perfect for machinability to fit onto my motor shaft and threaded rod, but they are a 15 and a 60 tooth set, so 4:1. It may not be ideal, but can I run the motor at approx 256RPM (4x64)? You mentioned earlier it should be fine for 2 or 3 revs per second, so how about 4

Cheers, and please bear with me!

 

The black dots represent common wiring points.... so they could be anywhere, not just in the middle.

What RB said about using the tab of the 7805 is a good idea, just use black wire from all the earth points back to this.

Connect the 1K resistor between the long LED leg on the switch and the other switch connector that goes to the Linistepper.

The short leg of the LED goes to GND.

There is no difference between GND and the symbol that was drawn.

For the 7805 I would bend the legs at 90 degrees and then loop the cap legs around them before soldering together.

For the fuse I would probably use a panel mount version, that way if it does go, you can easily replace it without opening up the box.

Don't forget to buy a fuse, they don't come with the holder! Oh and if you decide to use the 7805 tab as an earth common, I would probably buy some solder tags to make sure everything stays where it should.

You can get everything you need from bitsbox and it will work out cheaper. (I don't have anything to do with them just trying to save you money )

HTH Steve.

 

Ok, you may laugh at me but seeing as I am not versed in circuit diagrams, I would find it a lot easier to see this in the form of a physical diagram showing what wires go directly from and to. So taking Romans diagram and the edits, as well as the advice bance gave me on the LED power switch I have come up with this: (I have taken out the 3 switches from the bottom)

In physical wiring terms, does that all look correct?
I think I understand the concept of the black dot common wiring points - does the above suggest I do? I am correct in thinking I should not literally be making a T-junction out of wire rite??

As for those parts, I did check bitsbox, but I could not find an xtal or the in line fuse box.

 

Yeah, that looks good to me, just the ground leads should have solder tags and be bolted through the tab of the 7805 and your enclosure.

Bitsbox doesn't have an in-line fuse but they do have a panel mount, or a chassis mount, look under circuit protection, that's where the fuses etc. are.
The 16MHZ crystal is available under CRYSTALS fourth from the bottom 45p.
Solder tags are under 'Hardware'.

Good luck, Steve.

 

ok so the 3 ground wires I currently have going to the solder tag then soldering that to the GND pin on the 7805, instead should each have a solder tag which has the bolt going through that is holding the 7805 to the enclosure?

xtal = crystal, makes sense

 

Well the GND pin and tab are connected on the 7805, it's just a bit of a cluster f**k trying to solder all together on the one pin... it's easier to solder a tag to each wire and then bolt them together...

 

I'll disagree with Bance's last statement. I would leave the middle leg of the 7805 a bit longer, and the - legs of the cap a bit longer, and there is plenty of bare wire there (all grounded) to solder all the black wires to.

To Danstar10; yes those 2 things look fine, sorry about forgetting them. Did you want to get a 5x2 pin header as well?

A 2*5 female pin header will plug into the Lini control socket, here is an example of a 2*8 one (you can always cut them shorter with a hacksaw, I do it all the time);
http://www.ebay.co.uk/itm/5-pcs-2-x...195?pt=LH_DefaultDomain_0&hash=item27c9633b43

I have made a couple of changes to your wiring diagram, to simplify it and improve the current paths. Please see below.

I would not bother with tags as such if it is being soldered. Also the 7805 has no insulator and will ground your box too, which is fine.

Re the fuse I would put the inline fuse holder directly on the battery + lead, close to the battery if possible, say a couple of inches from the battery. That should give you good safety, and like Bance said don't forget to buy a couple of 32mm 1.5A fast blow fuses.

Also have a look inside your new multimeter, they often use a 100mA or 150mA small size (20 mm) fuse on the current measuring range. I would buy a few of those, as they are easy to blow if you forget to switch ranges on your mutlimeter.

With the xtal the two small ceramic caps go on the bottom of the PCB, each has 1 pin soldered to a xtal pin, and its other pin soldered to the middle ground pin.

You're getting quite an education, and likely some more to come with all the mechanicals!

I'm not sure if that motor will start or run well at 4 revs per second, it's possible it might have difficulties. The options would be to use lower gearing than the Meccano 4:1 set, or maybe to use a motor that has no internal gearbox...

 

Okey dokey, I have ordered all the above gubbins. I did get a 8+8 pin header to chop down anyhow
The wire I got was rated at 1.8A, 1kV (not 2A like suggested)

Cheers for the updated diagram

Bitsbox only had a 1A or 2A fastblow fuse, so I went for a 1A fuse, assume that will do the job, as I am not using close to that current?

Bugger, those shame 4 revs per second may be out of the motors range. What would be the result of that? The motor just not running, or overheating? The gears look really nice too! How about if I replace the 15 tooth gear on the motor shaft to a 25 tooth gear? I have seen a few of those on ebay. That would mean I would need 2.4 revs per second, or 144 RPM. Sound doable?

Cheers

 

... Bitsbox only had a 1A or 2A fastblow fuse, so I went for a 1A fuse, assume that will do the job, as I am not using close to that current?

That will be fine, average current when running is maybe 150mA and peak current should be well under 200mA.

...
Bugger, those shame 4 revs per second may be out of the motors range. What would be the result of that? The motor just not running, or overheating? The gears look really nice too! How about if I replace the 15 tooth gear on the motor shaft to a 25 tooth gear? I have seen a few of those on ebay. That would mean I would need 2.4 revs per second, or 144 RPM. Sound doable?
...

The result of speed too high is the stepper motor won't start turning. It's called "stall" and makes a nasty noise and is not good for the motor if stall continues for a long time.

The problem is partially mine sorry, I said the ebay geared motor was ideal based on your early mechanical photo showing a motor direct driving a straight threaded rod. Now you are going for a gear reduction and driven nut design the gearmotor is just a little bit slow.

It may do 2.4 revs/sec just fine, the test would be to program the Lini for that speed then connect up the motor and run it! If it starts and runs fine each time then there is no problem. Otherwise you could switch to a non-geared stepper motor of a smallish size that runs from 5v to 12v and the Lini code allows you to easily run that 64 times slower, so the nut gearing is no longer an issue.

Since you have come this far I would suggest test-running the gearmotor you already have, to get some experience and also for energy efficiency as that motor will have less battery drain than most options. And it really should not be that hard to find a gear of the right pitch and toothcount to get close to 1:1.

 

Hi Roman

Yeah I think I have sourced some decent 1:1 gears I can use which have brass hubs and plastic teeth, but the meccano ones I have now being made out of old aged brass look really nice
I think it makes sense like you say to test the motor and see what speeds it is capable of before deciding which gear set up to use, as I am keen to keep the meccano gears if possible, maybe swapping the 15 to a 25.

I have not received the parts from bitsbox yet, so I will likely not get them until monday earliest, meaning I can't wire up the 5v regulator yet...

For now it would be nice to get my head around how to flash the code onto the PIC. Is your offer to supply me with the code you wrote for a similar telescope project still open?

I have downloaded the MikroC PRO for PIC free demo, and have the pic programmer
http://www.ebay.co.uk/itm/190784296170?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2648

I'd need some instructions on how to go about compiling the code / flashing the pic etc.

Cheers

 

Quick update - turns out I got a late delivery and have all the parts.
I made a start at the 5v regulator circuit, however I found it very difficult to connect the wire to the header. I was trying to connect each wire to a small crimp, like this (after cutting the plastic bit off)
http://www.maplin.co.uk/insulated-crimp-ferrules-455091

then slot that over the header pin. Problem is the crimps were too big so I was trying to improvise by squishing with pliers, but it all got a bit messy. How would you suggest I attach the wires to the header? Would you just solder them directly?

I also managed to break the LED switch locking mechanism, so I have ordered a new one. All in all a frustrating foray, but I will try again when I get the new LED switch and hopefully a little advice from you guys

Also, I like the ideas bance had of grounding the wires to the 7805 via solder tags through the bolt, seems tidier and easier for me, is there any reason you advised against this Roman?

Cheers

 

Not to worry, these things happen, although I know they can be very frustrating.

Connections are one of the most difficult things to deal with, because there are so many different kinds, it can be very confusing...

The ferrules you were trying to use are often known as bootlace ferrules, they are normally used for stranded wire or to combine one or more single core wires for insertion into a screw fixing. Essentially they are a male connector.

Without knowing which connector you have on your board there is little help I can give towards guiding you in the right direction there.

How you managed to break the latch on the switch I don't know..... but if I were you I would buy a different switch, if that one give's so quickly it probably isn't up to the job!

As to using solder tags that's what I thought. it would be easier, given that you're probably not that used to soldering. I can't think of any reason why it wouldn't be ok.

I'll have a look at the BOM for the linnistepper and see if I can offer any more advice on the connector.

I'm glad Bitsbox came up trumps after all the hype, Ive been giving them... They haven't let me down yet!!!

HTH Steve.

 

Ok, the BOM of the linnistepper doesn't include a header, so you must have bought something else....

This is the type that most people would use, is yours like that? If it is then it should be no problem to simply solder on to it.

Actually there is probably no reason you can't solder directly to whatever you have, just remember to check afterwards that there are no solder bridges.

Good luck, Steve.

 

bance - the part I was having trouble attaching wires to was the 'double row socket' I ordered from bitsbox and then cut down
http://www.bitsbox.co.uk/connectors/header_con.html
which then plugs into the IDC 10 pin socket on the linistepper.
http://www.piclist.com/techref/io/stepper/linistep/LiniV2_bld.htm

Yeah bitsbox have been great so far, thanks again for the link

I think i broke the switch by trying to force it into a hole in the enclosure that was just a little too small, as I do not have the correct drill bit. I am working in my bedroom in a small flat in london, no garage and very limited tools!

Cheers