ZoneMikel's Blog

Multisim

While creating the mainboard in mutisim I discovered a lot of errors in the thinking. For one I was using N channel mosfets and not allowing things to go to ground where I should have been using P channel. One example of this was the voltage input jack for charging, had I simply not allowed it to go to ground it would have still went through the batteries to ground. So I replaced the two N’s with P’s, this actually helped clear up some stuff. One thing it cleared up was the on push button, this button would have needed ~1v to turn on had it been a N channel so this would have required some voltage divider and a constant drain on the batteries to provide this 1v, but with the P channel all we need is the tactile switch to go to ground. Also another thing that was wrong was we had the mosfet that keeps the circuit on before the place where the battery taps in, this would mean the motors would flow through this mosfet which isnt rated high enough this would burn it up. All these modifications will have to be updated in the architectural design and the pinouts and such. Another thing i had to move the mosfet that turned off the circuit to before the 7805, i dont want the 7805 running constantly.

I also had some trouble with footprints. I had to make a footprint for the pots i ordered from ebay, also some things didnt really have the pins mapped right. Like the Voltage Regulator, pin1 vin, pin2 gnd, pin3 vout and that is how it was shown on the symbol but then when you sent it to ultiboard the footprint had things going to the wrong pins. I had to go through and make sure all those things were ok. I pretty much just spot checked a few things to make sure the pins were going where they should.

I tried to make the multisim design as “pretty” as possible but that proved impossible. I added all the male headers and other circuits into sub circuits but even that was not enough. The circuit has so many connections you cant really tell what goes where, well i take that back you can but it takes a lot more than just glancing at it to see where the wires go. I’m not sure what can be done about this except being very careful. I tried to move one of the components after wiring it all up and it made all kinds of messed up connections all over the place causing me to start again from scratch. I tried to make some of the connections more clear by making them at a angle, when two things overlapped I set one at a angle.

Ultiboard

Things didnt get much funner when I moved everything over to Ultiboard. I spent a long time trying to figure out how to get the “autoroute” and “autoplace” to my liking. If you autoplace the components it kind of just throws them around without any order, this might be great for connections but it makes a really nasty confusing board. I wanted the connectors to be on the outer ridge and the components to be more on the inside, also the led’s and buttons should be in a easy to find place. To acomplish this I put everything where I wanted it and then locked it in place. Since I’m going to be having a double sided board I allowed smd mirroring, then I allowed ultiboard to autoplace the components. There are a lot of things that are needed to know to get this done without taking all day, it just comes from experience working with the software and reading the help files (and user guide on your c drive).

After that I wanted to route things on both sides but it always seemed to autoroute more on one side. I found that you can fix this by selecting the nets in the spreadsheet (on the bottom if enabled) then where it says something about what side to route on you click that and then click top and bottom, make sure its not grayed and checked make sure its clearly checked (by checking it a few times). This causes the mode of routing for the nets to be 111 for a double sided board and then it will create a ton of vias and route a lot on both sides of the board. I had to reduce my trace width to about .3mm which is pretty small, also I had to reduce the clearance in the traces to about .1mm i think. The traces get spaced out well by changing the density factors in the autorouting settings. I recommend reading the ultiboard documentation (or help file) thats here \pathtoNI\documents\ultiboard usermanual.pdf . You really have to read that to know what all the “cost factor” things are when setting the settings for the autorouting and autoplacement.

Auto routing got me almost all of the 130+ connections, then I added a few jumpers and added a little fluff around the places I know I’ll have to work magic later. I paid special attention to the accelerometer area because I wont be able to solder jumpers to this area later. At the least if you see parts of the ratsnest where you will need to solder jumpers later make sure there is a nice copper trace there to solder too. I think I’ll have to add about 10 jumpers but they are all in places where I can get to. At least the board has some order to it and it will be easy to work with when/if everything works.

There are lots of errors I’m ignoring especially around the lga-14 footprint since its pads are closer than the clearance for the boards. I’m hoping to make the traces a lot fatter with a marker after transferring to the board, we will see how it goes.

Oh just a quick note. I was looking for a way to print out all the connections to test them by hand however I could not find it anywhere in multisim. But, if you export the circuit from multisim to orcad pcb (transfer -> export to pcb layout) then save as a orcad .asc file it creates a file that you can open in wordpad. In that file you can easily see what is connected where, its very useful for checking everything.

This has been abandoned.

This board was very hard (impossible?) to make. I thought of a better way of doing this using several small boards instead of one big one. You can read about the modular board here.

1. ZoneMikel's Blog » Blog Archive » Modular Jinx mainboard says:

   May 26, 2010 at 9:49 pm

   [...] two sided big jinx mainboard was kinda a disaster. With traces just .3mm thick and clearances of .1mm I think I was pushing it a [...]