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LED bargraph mWattmeter ......Very useful for a uBITX or BITX40.
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I'm off looking at a very inexpensive standalone LED bargraph mWattmeter with a 25W to 25mW (30dB) range using the cheap AD8307s, but there are apparently MANY MANY different implementations and desires out there. Might be worth another "Topic" ......hard to tell from this huge list of "Topics" ;o).....heck, here is yet another "Topic". Useful and focussed on the uBITX or BITX40.
Lets try no microcontroller (and firmware) and just a basic LED bargraph display ......first. Comments ? input ? suggestions ? 73 Kees K5BCQ |
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Seems that a simple LM3914 bargraph driver coupled with a log detector like the AD8307 might be easier to build than using a micro-controller and writing software. Arv _._ On Tue, Jun 19, 2018 at 12:24 PM <Kd4epg@...> wrote: Let me know when this is available.. may need 3 or 4.. |
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Jack Purdum
I don't know about the hardware, but I wouldn't think the software would be that difficult. Jack, W8TEE
On Tuesday, June 19, 2018, 2:40:16 PM EDT, Arv Evans <arvid.evans@...> wrote:
Seems that a simple LM3914 bargraph driver coupled with a log detector like the AD8307 might be easier to build than using a micro-controller and writing software. Arv _._ On Tue, Jun 19, 2018 at 12:24 PM <Kd4epg@...> wrote: Let me know when this is available.. may need 3 or 4.. |
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Take a look at this project for enough good ideas to get you started. Uses the 8307 and the 3914
Years ago I built something similar (not using the 8307) The 3914 is a ratiometric device, so if you feed in a forward power signal as its reference, and a reflected power signal as the measured quantity you'll get a rudimentary SWR display N5IB |
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Arv,
You are right on. Local AQRP position: I think the benchmark for what is useful?and sells as a kit ought to be the mWattmeter III which is based on our earlier mWattmeter II (88 sold) ......it has a Stockton Bridge, uses a (painstakingly prepared) lookup table......which Ben and I don't want to do again, minimal microcontroller, and 16x2 backlit display. It sells for $41.95?without a case. The way I see it; you either come up with like function/capability (Nano microcontroller, 16x2 backlit LCD, etc) at 2/3 of that price (~$30) or you come in with less function/capability (LED bargraph, LM3914(s), no microcontroller) at a much lower price (<~$15). Both including an enclosure. 73 Kees K5BCQ |
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Kees For a wide power range watt-meter it may be necessary to use a digital readout simply due to more watts being covered.? Digital readout provides finer resolution as long as the measuring circuit is as accurate as the readout resolution. For a QRP watt-meter it seems that less readout resolution can be tolerated if we are only wanting to see if the rig is putting out 0 to 5 watts.? The AD8307 would convert analog input to log-scale (decibels) and a bar-graph would show rather gross changes in power level.? Also could have range switching with the bargraph display to cover multiple ranges or multiple resolutions. I agree totally that using a real bridge (Stockton, Bourne, or similar) is necessary if we are to know how much power is going out versus how much is being reflected.? Given the sensitivity of IRF-510 devices to impedance mismatch, this may be of prime importance.? From that, there seems to be two directions of discussion, (1) a dummy load and attached watt-meter, and (2) an in-line bridge and adequate readout for protecting the RF PA from mismatch. There is also the issue of most BITX designs not having a low power output mode that can be used for tune-up purposes. Not sure yet what to do about that situation. Arv _._ On Tue, Jun 19, 2018 at 3:24 PM Kees T <windy10605@...> wrote: Arv, |
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