Friday, July 30, 2010

More sequencer planning

-"I will try to buy as few components as possible"
Who said that?!

Ok, so I had a feeling from the start that this would rather turn into a "I hope I can use some components I already have" rather than the above...

I spent a couple of days trying to fit the panel layout to a plastic sweets box. I made a layout in InkScape.

LOL the background is transparent.
Please click the image to get a white background, assuming that is your default browser background ;)

I need something to build it in
Readily available enclosures for electronic projects cost a FORTUNE. I have no idea why but finding boxes that usually cost more than you'd pay for a product of the same size is not uncommon. So, I found this polystyrene fully transparent box at home that used to contain Ferrero Rocher sweets (omg they're good!)

Ok, it will probably crack when I try to open up holes for the buttons but at least I have decided in the dimensions for the panel. If I screw it up, I guess I can buy some clear acrylic sheets or something and make a box of my own. But for now, I'm sticking with this. ( I know I will break it... )

Ok, now I know what to build it in. What do I put in it?
I drew an almost complete schematic for it in Eagle and identified which components I need.

(Yes I know it's unreadable but it's just to show the basic idea, not details, since they're not final and some are even wrong anyway)
Like I said, I know there are errors here, for example (start/stop/clock select LEDs occupy same address space as the beat LEDs). No pullup on the data bus...

The trigger input (for running the sequencer in slave mode) will have a dedicated pin on the PIC. I forgot to make room for the output gate but I realize I have no available pins for it anyway so I think it'll have to be an addressable output just like the LEDs. I have some 4 bits that are still unused I think ;)

The DC input will not be +5V as drawn but probably +6V instead. Why?
I will have a voltage regulator for the PIC and logic chips (perhaps 3.3V, not sure, maybe a small switched one so I don't get a lot of heat in the box?). Then I'll use the DC input for the 5V reference (for the DAC reference voltage).

Also, the ICSP connector part will change to just use physical switches for the Vpp and Vcc pins as well. That way I don't have to mess around with extra diodes and stuff for the PIC to isolate the circuit Vcc from the programmers Vcc etc...

So.. Lots of buttons, some different colour keytops (they didn't have any blue ones in stock so I ordered black instead :( ), some 7-segment BCD LED drivers, a D/A converter, some jacks for connecting DC voltage and CV and gate cables, and some experiment board to mount all the panel components on.
I placed an order at DigiKey. Excellent place!
Even though it's in USA they have free delivery (worldwide) on orders exceeding 65 Euro. My order ended on 100 Euro and 88 cents. Placed the order on Tuesday 27th in the morning and had a UPS guy (woman actually) delivery it to my door Thursday noon. Two days from USA to Sweden :) Of course I additionally had to pay about 25 Euros in taxes when the parcel was delivered.
So, the first order I made already cost me about 125 Euro :P

This will be a 2-floor design.
Top card will house all the panel components (buttons and LEDs) and will probably be made out of the two experiment boards (hope they're enough).
For the bottom card I am seriously considering having a PCB manufactured. It's going to have a LOT of 8-bit databus cables all over the place otherwise.
The two cards will join using long pinheaders (bought some 15mm long ones from DigiKey) and I hope I won't have problems with glitching connections.

Next step will be to build the panel board (at least place the components and connect them). Then when I make the lower card I have to see where to place the connectors on the two cards. I am hoping it will be smaller than the panel card at least because otherwise it will be very expensive.

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