And so it begins...

[moorejl57]

Hi All, my first post, been lurking for a week waiting for my MPP kit to arrive!

After contacting Sven about his Mirage project, he pointed me to this site, the diy detector site and suggested I start with the MPP Beach. I just received the board and parts kit, a Whites space saver rod kit (very nice for the price), fiber bolt, 100' 24 AWG enamel wire, thin copper EMI tape and a Proster LCR meter (works pretty well).

I built my first ever coil by 3D printing a 170mm wide 8mm octagon with a hollow cavity for the wire and a slit on the outer perimeter to feed the wire in. I used the coil calculator to target 325 uH using 26 turns. The LCR meter reads it at ~328 uH, resistance right at 2 ohms, resonance at ~864 kHz with copper shielding in place and no lead wire. I am very happy with this first attempt even if the coil is a bit on the slow side. The 3D printed "donut" holds the coil together and provides a spacer between the coil and the copper shield. I think the dielectric constant of PLA is about 3.5. The calculated capacitance is about 103 pf.

Question:
I am looking through the build manual and see on step 4, that you measure the flyback voltage across the damping resistor which should be in the neighborhood of 350 V. My scope has a input limit of 300 V, will this be safe to measure with a 10X probe? If not, what do you suggest I do to measure this.

Jamie

[mushaba]

Question:
I am looking through the build manual and see on step 4, that you measure the flyback voltage across the damping resistor which should be in the neighborhood of 350 V. My scope has a input limit of 300 V, will this be safe to measure with a 10X probe? If not, what do you suggest I do to measure this.

Jamie[/QUOTE]
Hello Jamie and welcome to the forum.Make sure to switch from 1x to 10x on the probe and then via menu set the channel probe settings according to 10x.

[Qiaozhi]

Question:
I am looking through the build manual and see on step 4, that you measure the flyback voltage across the damping resistor which should be in the neighborhood of 350 V. My scope has a input limit of 300 V, will this be safe to measure with a 10X probe? If not, what do you suggest I do to measure this.

Jamie

My scope also has an maximum input voltage of 300V, but I've never had a problem measuring the flyback voltage, even when much higher than 350V. Make sure you use a 10x probe. Even though I have sometimes (accidentally) had it on the 1x setting, nothing went up in smoke. There's most likely some protection diodes to take care of any excessive voltage.

[green]

I have a Rigol DS1052. Zapped a probe with it on x1 when measuring fly back, probably around 450V. Don't forget to switch probe to x10.

[moorejl57]

Thanks everyone for the advice, I will be sure to use the 10X setting.

[kt315]

guys do suggestion of Eric where he wrote to put a resistor 1Ohm in serial to coil and look a picture on it.
thats enough and you do not need setting x10. just read all that Eric had wrote.

[moorejl57]

So you are suggesting that I limit the current and magnetic field with a series resistor such that the flyback voltage is smaller and then safe for my scope. Sounds like a reasonable alternative, thanks for the input.

[6666]

Just use a voltage divider across coil

[kt315]

So you are suggesting that I limit the current and magnetic field with a series resistor such that the flyback voltage is smaller and then safe for my scope. Sounds like a reasonable alternative, thanks for the input.

flyback voltage is almost sure same. you will see a current. put a resistor between the coil and +9V. put gnd cold end of the probe on +9V, hot end on the
joint resistor-coil.

[moorejl57]

flyback voltage is almost sure same. you will see a current. put a resistor between the coil and +9V. put gnd cold end of the probe on +9V, hot end on the
joint resistor-coil.

Oh, I understand what you mean, measure the smaller voltage across the series resistor, thanks.

[moorejl57]

Just use a voltage divider across coil

Seems like this could work as well, thanks.

[moorejl57]

New question:



On stage 3, while installing components
1. C22 is ceramic disk vs. little white box type, not trying to nitpick, just want to verify substitution is OK

On stage 3, while adjusting TX pulse period and width, are these normal expected observations
1. set pulse period first, while setting pulse width observed that pulse period is also changing (settings are interacting)
2. pulse period is not completely stable (varying at a relatively slow rate (slow period jitter)

[moorejl57]

OK, I am passing stage 4

Flyback well over 350V, hard to measure but probably around 450V. Still have an intermittent jitter on TX oscillator period.

[moorejl57]

Stage 5 waveform at TP3, does the noise level look normal?

[Qiaozhi]

Stage 5 waveform at TP3, does the noise level look normal?

The noise level looks ok. If you change the orientation of the coil you should see the noise level change, indicating that it's externally generated.