Getting close to Beta now.
I have just spent a week tracking down a mysterious 256 Hz low level (30mVpp) tone that ended up being a software configuration error in the DAC initialisation code! However before that I thought it was a noise issue caused by PCB layout, or the wrong sort of bypass capacitor. I also popped another uC looking for it, costing a few days while I had the dud uC removed (thanks Matt) and I loaded a fresh one. Think I better stick to software…..
To get to the bottom of the problem I partially loaded a “minimal” 3rd SM1000. Just enough parts to make the uC run the dac_ut unit test program, power supply bypass, STLINK, crystal oscillator, boot mode resistors. Only about 1 hrs soldering, quite remarkable really.
Here is the mysterious triangle wave:
Michael Wild DL2F2 in Germany has built his own SM1000, using a PCB I sent him and the parts off our Digikey BOM. That’s a pretty exciting confirmation of the design. Having a another unit running has been very useful when making comparative tests. Here is Michael’s SM1000:
Michael, Rick KA8BMA, and Matt VK5ZM have also been very helpful in suggestions when I have been debugging. Thanks guys! Matt has also been explaining to us how ceramic caps can lose up to 80% of their C as their working voltage is approached. So best to use tantalum or electrolytic capacitors for noise sensitive applications like power supply and analog rail filtering (e.g. C25, C28, C29, C10, C12 on the SM1000). I could hear the noise drop when I soldered an electrolytic capacitor across C25 (input to the SM1000 switching power supply).
Right now I’m trying to reduce some remaining noise sources and soon hope to test over the air to see how the SM1000 works with large RF fields nearby, and also ensure it works OK with a couple of HF radio models. Rick is busy updating the schematic and PCB with a bunch of small changes we have picked up working on the prototypes.
We have a quote for the Qty 100 beta run, and are still on target to ship SM1000s in 2014. As soon as we have completed testing the prototypes we will kick off the Beta run and I’ll start taking pre-orders. Lots of work required on the software, but I figure that can wait until the Beta hardware is getting made. I want to take the open source approach of release early and release often, and that means getting betas into your hands ASAP.