Another pattern generator

[Mike Watterson]

I like the R-2R apart from the fact it's easier and may be higher precision due to tracking.

[`FRANK.C]

I will have a play with a R-2R ladder, but it may be a few days before I get a chance.

Frank

[`FRANK.C]

I decided it was time to wrap this one up. I had a play with a R-2R ladder which is undoubtedly more accurate but I decided to keep to my original design this time as it left the PCB layout easier. I would have to change around pins by rewriting the program to make the R-2R layout as easy.  I did up a PCB for it and bunged it in a box. Pictures of the completed project below.

Frank

[ppppenguin]

Very neat. And surface mount DAC too.

[`FRANK.C]

Thanks Jeffery
I wanted to get a bit of practice in with SMD's as it seams that that a lot of components are available only as SMD's. I find so long as you stick to the larger sizes they are not too difficult to work with.
I had intended to build it on a single sided PCB but as it turned out I only had double sided to hand.

Frank

[AlanBeckett]

A splendid job young Frank.
How about selling PCBs and programmed PICs?
I used to have the wherewithall, or at least the Company did, but not now.

Alan

[Bush Radio]

Like Alan, it would be great to have a pre-programed IC and a PCB.

Dave

[`FRANK.C]

Hi Alan and Dave
Unfortunately that's something I am not able to do, but I am making the hex file for programing the PIC available free to anyone that wants it. If anyone wants to program PIC's and sell them on, that's fine by me. The hex file is supplied as is and without any type of warranty. When I get a chance I will put a page up on my website so it can be downloaded until then if anyone wants it just send me a PM with your email address.

A pdf of the PCB is attached, it should print out at the correct size. It is mirrored as I use the laser printer method for making PCB's.
The PCB suits a Hammond 1593KBK enclosure.

Frank

[Mike Watterson]

It wouldn't hard to build this on strip board, and optionally use R2R DAC ladder and all through hole parts, though SM resistors work fine on the copper side between tracks or across a cut. No changes to code needed.
A clone PicKit2 USB programmer is cheap from China. Put 6 pin header for the programming cable to PIC on the stripboard.

Lovely project Frank.

[`FRANK.C]

Thanks Mike

As Mike rightly said it can be easily be built on strip board etc.  Just keep the tracks as short as practical, particularly around TR1's base and the track the connects R1 through R8, extra self capacitance in this area will reduce the bandwidth.

A different DAC arrangement can be used. All outputs are at logic level. One DAC is needed for Pins 11 to 14 which produce everything inside the circle and another DAC is needed for pins 15 to 18 which produce everything  outside the circle. Only one DAC at anytime is active, with the pins supplying the inactive DAC being high impedance .

Pin 4 produces the syncs, logic 1 = blanking level, logic 0 = sync tips.

Just had another look at the circuit I poster earlier and I see a mistake, R11 dose not exist, it should be a wire link.

I would go for a Pickit3 instead of a Pickit2. I originally had a Pickit2 but it did not support all the PIC's I wanted to program so I had to get a Pickit3.
I don't know if a Pickit2 will program a 18F24K22, it may not.

Frank