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The max hash rate with my firmware is achieved at speed=1650 to speed=1750-1800 which may not be the same as the chip's operating frequency but it yields precisely that hashrate
I've been using your firmware and found personally this isn't true at all. I'm still around 1280 .94V, my two boards running on Debian run around 10 GH/s. The other 2 on raspberry pi, Archlinux run at 17 GH/s. The bfgbuild, drivers and firmware are identical. I've confirmed these speeds on both multipool and givemecoins.
Can someone confirm that shorter and higher quality USB cables yield higher speeds? I'm not entirely sure yet but this may be the most cost effective upgrade you can make. I also appreciate the change to the LED.
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It's hard to measure DVDD current directly because the current is high and because it's hard to break DVDD circuit at one location in order to insert an ampermeter there.
I agree, I'm considering moving the regulator to a breadboard in an attempt to get a more accurate measurement of the output current unless someone has a better idea. An easier method might be increasing the resistance at Pin 11 (sense +) through TP1 on the regulator and measuring the change in voltage to get a better idea of the output current. Things like that work in my head, but don't always pan out in the real world. Have you had any regulators fail yet?
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Our thermal design is very capable, involving heatsinks on both sides of the PCB. The thermistor was physically attached to one of the per-chip top side heatsinks and protected from forced air cooling by a layer of glue and a piece of plastic, so as not to distort measurement results due to sensor cooling. The top side heatsinks were also not very hot on touch. However, these results may still be inaccurate because of the very nature of measuring temperature with thermistors. I'm going to try the more accurate chip thermal sensors, namely MCP9700A. Also there are no means of measuring the chips' junction temperature. With heatsinks occupying all the space around the chips, you could only mount a thermal sensor on the heatsink, and then your results will depend on quality of thermal coupling between the chip and the heatsink. So even with better sensors, any temperature measurement of this kind should be considered only approximate.
I favor the method of holding my hand slightly above the heatsinks, I've suspected via IR gun that the reported 25C is closer to 30 on my boards. I might be able to borrow a slim PRT that could take this measurement pretty accurately. Like you said all temperature measurements utilizing resistance in this method are approximate. Utilizing a 4-wire resistance and an ice point reference is probably the cheapest. I cut up a 10 ft hunk of aluminum C-Channel from the Home Depot and thermal pasted it
