Thanks Hans,

It's an odd one then.? I certainly uploaded the Tips doc ok, then next time it was no upload button.

Needs a mail to groups.io methinks.
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Rob G4NQX

John, It sounds like the screeching and dimming is caused by the power supply falling over when the IRF starts drawing heavy current from it. It may be due to the gate bias being set a little high and the IRF going into avalanche. (that's why it stopped when you turned the bias down) Is your power supply beefy enough? Although you probably won't need more than a couple of Amps it's nice to have some headroom. Bear in mind many 'Overseas' brands rather overrate their specs! PC power supplies are a great, cheap, alternative to expensive lab supplies. but be carefull, they can supply a LOT of current if you short something! (Fuses are your freind!)

Also, I'm not sure your ammeter really has the resolution to accurately set the bias current. It might be worth using a current shunt resistor to measure it with. Dig around in the junk box (or somebody elses!) for a 1R 15W power resistor (or something close) stick it in the PA power line and measure the voltage between the resistor's terminals. Using the magic of ohm's law (I=V/R) you have your current measurement.

Hope that might be helpull, I'm no expert by a long way, but i'll help you out if i can.

开云体育

Sent from my iPhone

My suggestion would be get a novice licence to start. Kb6nu has excellent courses for all exams.

That would be a good introduction to what you're getting into.?

Paul kk4ptv

Art,

Are you using 3.5 inch or 2.8 inch display. Code is written for 2.8 and will take some scaling to fit properly.

I'm using a 3.5 inch mcufriend here on a twin signal generator project and it's 480 x 320. (Notoriously difficult to photo)

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Rob G4NQX

开云体育

Why does the answer come up as you post !!

OK i found what I was looking for.? The contrast pin is current driven, not voltage and requires 200uA to be drawn to keep the contrast just so.? Grounding the pin via a variable resister brings the current draw up to requirements and provides contrast.

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Rob G4NQX

Talking of lcd contrast.

I usually wire up as a voltage divider as I've always known it to be.? First pic.

By accident on the breadboard I plugged the 5v wire in an empty row, so the pot didn't have a 5v supply. Pic 2.? To my surprise it works ok with no problems.

I've searched for an answer as to any harm but most results say voltage divider.? Anyone really know why pic 2 is considered wrong ?

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Rob G4NQX

The moderator or owner of the group can set the permisssion to upload files to 'ALL' in the group.? This was reset at maintenance and could be reset back.

HANS ,? ASHHAR ???? Where are youuuu........

Please could we have upload back.? We promise to be good boys or girls ! Honest !

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Rob G4NQX

How would you solve the issue of some new ham with a voltmeter and a Bitx40 that doesn't quite work?

If I were to advise a new ham with just a voltmeter, I'd tell him he needs to learn to walk before he can run, and that if he wants to get into home brewing he should start with something less challenging--for instance a DC receiver kit with a good track record of successful builds. Then maybe get an Arduino and monkey with that a while. Get it to display his call sign on an LCD, play with one of the ADC channels to read the value of a pot, stuff like that. Then get an Si5351 board from Adafruit or Etherkit or QRP Labs and get it to make some RF. He can verify it's working by using the receiver he built.

By now, he (or she) is getting excited because there's been some accomplishment feedback (always positive, never negative) and some sense of making headway. So now he has a signal source and he knows a little MCU programming. Now maybe he can make a simple diode peak-detector type RF probe, and if he wants he can use the ADC in his Arduino to display the probe's reading (compensated in software for the non-linearity of the diode). I suppose he could even get an AD8307 and read the output of that with his Arduino (once he learns a little about logarithms--a Wikipedia article will do for starters).

In the meantime, he's reading everything he can get his hands on about common-emitter biasing, double-balanced mixers, low pass filters, and the difference between resistance and reactance. Before he's hardly aware of it, he's off and running. He might buy one of those cheap-but-good-enough LC meters from China, and if he was still taking my advice I'd suggest he consider springing for an inexpensive oscilloscope--even an old analog one. This will kick his experimenting, testing, and troubleshooting capabilities into high gear.He'll at least know he'll need an SWR/Wattmeter and he might even put one together. They're nice, simple little projects.

*Now* he can take the BitX40 off the shelf and know enough and be equipped enough to make a go of it, and in place of newcomer frustration and discouragement will come some real satisfaction.?

That's how I would solve the problem of some new ham with a voltmeter and a Bitx40 that doesn't quite work.

73,

Todd K7TFC

Got it John. and that is why my second post immediately.

?regards

?sarma

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