FYI, when we tested the DirkCheapSSR prototype we tested indoors with varying length cables. We tested up to 150 feet with stranded cable and it still functioned accurately. And because the SSR was developed in the spring (well after the freezing temperatures had left) no temperature-based testing was done. Given the chip's spec dips down to -40C, we didn't expect that temperature would have much bearing on the VO2223a chip's performance -- at least not the *normal* temperatures where people live, anyway.
Our initial resistor selection (per the specs) was 120ohms, and the chip performed perfectly. However, at this level, we felt the chip would be too close to the limit of current a PIC could either source or sink, so we tried other values. We tried 330 ohms and that worked fine, too, but the total current would still have been too high for the SimpleRen32 to manage. Mathematically, the 680 seemed to be a good match for the SimpleRen32, and it was common to most all other SSRs on the market. We tested both 100 and 150 foot cabling with the SSR each time we changed resistors and we found it to perform adequately.
What we did not test were various configurations of controller/power supply combinations insofar as our standard (here at DIGWDF anyway) is to use a power supply that provides at least 200% of the required base current required by the controller or device. Consequently our test bench has 1.5A , 3A and 5A power supplies and/or transformers. (This concept seems to smack in the face of our MiniRen controllers which use a 300ma Radio Shack transformer, but 300ma is more than adequate for those small, wireless 4 and 8-channel controllers and that transformer was primarily chosen for its small footprint.)
We have built DirkCheapSSR's into some of our own display pieces and have not experienced any of the issues users have expressed. That said, we do locate our controllers outdoors in centralized locations relative to the display pieces they are assigned to control. This effectively minimizes the length of all cable runs. We also power many of our controllers with a 1.5A 6vac wall wart (see photo). We like it because it is compact enough to fit inside the same CG-1000 cases common to so many DIYC projects and because it provides ample current and voltage (actual measured voltage is 7vac) too. At 1.5amps, we never worry that our devices will suffer from a lack of current.
We are saddened to read that users have encountered these issues with the DirkCheapSSR, and we're encouraged at some of the creative and helpful comments shared by users who've found some nice workarounds. Shorter cable lengths makes good sense, as does lowering the light intensity, and certainly, changing the resistor can make a difference, too. Even soldering another resistor in parallel with the 680 will effectively lower the overall resistance, so you don't necessarily need to remove the 680 to change the resistance to a lower value. For example, soldering a second 680 right next to the existing one equates to a resistance of 340 ohms.
In any event, we felt it may be helpful to some users to know how we use the DirkCheapSSR ourselves and how we power our electronics, and we wanted to post the information.
mg:
