Replies to Minipulse Plus

[Davor]

Depends.
Ceramic caps pose very little inductivity, and hence they are good for RF filtering jobs, but they suffer from non-linearity, and piezo-like effects. I still have a few that I keep for educational purposes that buzz quite audibly when audio is applied to them. They have abysmal distortion, and yet, they are not too bad for RF. The only place for those in metal detectors is decoupling.
Polys are OK for audio, but at large capacitances they grow too big.

[eogeo]

Thanks for the feedback Davor. I will put ceramic caps further down the list.

[greylourie]

This is a very interesting topic that has been puzzling me a bit. I have seen a P.I circuit which makes use of 2.2uF poly with 22.5 mm (or similar) spacing, for the SAT. But when I look at other circuits for a point of reference, I cannot find an example using such a similarly substantial cap. So what I was wondering, is there anything wrong with using larger value poly caps other than the physically large size and subsequent constraint it might pose on circuit layout and pcb real estate ?

And I faltered when trying to modify and place a 2 pole filter in another (Goldscan) circuit, when I ended up with a large cap value for the first stage - whilst trying to maintain close to original R / impedance values. KingJL seemed happy with using 1uF in part of his 2 pole filter for his modded Hammerhead.

Is there a rule of thumb, or guide to the min/max values of poly caps for use in LP/HP filters for P.I receive chains ?

[Davor]

Basically it is only size, and perhaps cost. Otherwise they are quite nice.
They have quirks of their own, but you'll hardly notice any at metal detecting frequencies.

[greylourie]

Thanks Davor.

[satdaveuk]

Just received 3 PCBs today from Siverdog. Once I've got the components together I'll build one unit to check everything is OK, and then write a "build document" to try and prevent the same failures that Surf-PI builders are experiencing.
Be patient though, as this is very much a background task.

Hi
opened your gerba files ok and found very interesting, well done
If there is going to be along delay in getting lay files for your rev b may deside to use rev a and just change relevent mistake 4"x3.5" is a ok size for me, top layer copper print is easy bottom I need to spend more time on getting it black and white.
How is your test Jig fairing? because im eager to start experiments, dont care if its got teething problems , got all the bits although my MC14538BCP has a G on the end , but should be ok, what do you think?
Regards

[Qiaozhi]

Hi
opened your gerba files ok and found very interesting, well done
If there is going to be along delay in getting lay files for your rev b may deside to use rev a and just change relevent mistake 4"x3.5" is a ok size for me, top layer copper print is easy bottom I need to spend more time on getting it black and white.
How is your test Jig fairing? because im eager to start experiments, dont care if its got teething problems , got all the bits although my MC14538BCP has a G on the end , but should be ok, what do you think?
Regards

The test unit is working fine, but Silverdog is currently very busy and having difficulty finding time to replicate the design.
There are a few errors that need to be corrected in the wiring, plus some component changes. That's why REV-A boards will not be made available.
Please be patient and wait for REV-B.

[WM6]

Did I miss power consumption info? Thanks for check Qiaozhi.

[Qiaozhi]

Did I miss power consumption info? Thanks for check Qiaozhi.

This will depend on the TX pulse rate and the pulse width, but with the current settings (1000pps and 57us) the current consumption is 87mA.

[WM6]

This will depend on the TX pulse rate and the pulse width, but with the current settings (1000pps and 57us) the current consumption is 87mA.

Pretty low for PI, thank you.

[Qiaozhi]

Pretty low for PI, thank you.

This is how the Minipulse Plus version is set up at the moment. You can change the TX pulse width for get more depth if you wish, but the battery consumption will also increase.

[sinclairuser]

@ george- the mc14538bcp used in the minipulse plus goes down to 10us,i have in stock some mc74hc4538a(ceramic) its pinout is identical.
it is in fact the same chip its lowest setting is 1us,now if i use this chip 0v may not corespond to 10us and it will be harder to setup but should enable the MPP to go sub 10us(in theory as 10us is the limit of the mc1453).
do you think using a chip with a wider adjustment range will need any other considerations other than the setup issue?, i have six of these chips and no real use for them, the specs are so close it would be a shame to buy chips if these work or even work better, what do you think?.
@ satdave uk- the g suffix is for lead free.

[satdaveuk]

HaHa well it wont be for long because I use lead solder

[Qiaozhi]

@ george- the mc14538bcp used in the minipulse plus goes down to 10us,i have in stock some mc74hc4538a(ceramic) its pinout is identical.
it is in fact the same chip its lowest setting is 1us,now if i use this chip 0v may not corespond to 10us and it will be harder to setup but should enable the MPP to go sub 10us(in theory as 10us is the limit of the mc1453).
do you think using a chip with a wider adjustment range will need any other considerations other than the setup issue?, i have six of these chips and no real use for them, the specs are so close it would be a shame to buy chips if these work or even work better, what do you think?.
@ satdave uk- the g suffix is for lead free.

The problem with trying to sample at sub-10us is that you'll need a fast coil, and the preamp gain of 60dB isn't going to help either. Also, sub-10us means more problems with ground mineralisation, and the requirement for a ground balance circuit, etc., etc.

[sinclairuser]

yes i thought as much, i was not intending to run the MPP sub 10us, i was going to run at the 10us baseline, its a simple case of having these chips which are ceramic high quality originals, i doubt any i buy will be as good.
i think what i will do, is buy stock of the correct type build it with quality sockets, then have a play when its running as intended, if it does not work i will hard solder the correct chips, and leave it at that, i will report back regardless of the outcome as someone all ways starts asking about alternative chips.
at least we will know if the wider spec chip works.