Makro Racer 2 scheme

[ozzy_sv]

Hi
The scheme is not complete.
The digital part did not draw because it does not make sense without the program.
Voltage converters for the audio amplifier and converter from the battery to 5.5 volts also did not draw, there everything is clear without a circuit.


makro2.pdf

in jpg click on the picture to enlarge




Internal spare parts for armrest






Base board

[Skippy]

Thanks for posting.

For those like me who have trouble with the PostImage site, here's the schematic direct link:
https://s26.postimg.org/dr6g0rfl5/makro2.jpg

There's some interesting features in the circuit. The second RX amplifier stage has a wide range of gains ( x1 to x 0.1 , approx) , which presumably help cope with a wide range of ground signal level, including wet beach work. Though it does make me wonder why they had a problem with coil overload with the earlier Racer 1. Poor coil nulling? Or electronics with just too much gain?

The centre-tapped TX coil gets round the problem of low supply voltage, much like the Teknetics T2. It looks like the power to the coil is shut down when the CPU is not driving the TX switchover circuitry, there's a voltage-doubling rectifier (to detect AC) controlling the 4.7V regulator ON/OFF. It saves using another CPU pin.

The power rails have had some effort put into them. Many of the IC's have small series resistors, 10R etc to give additional noise filtering, and to help isolate each stage from another.

The 'battery box' PCB, with the switch-mode pre-regulator and the audio amplifier on it, is very much like the Tek T2/Fisher F75 design. Tek have their regulator set for 6 Volts, this Makro is 5.5 Volts.

[ozzy_sv]

who have trouble with the PostImage site

ups , I uploaded a file to the forum and pdf version in firs post have best resolution



Based on the photo from the internet in the first version of the makro racer there is gain control but it is performed on a digital resistor
Something like AD5175 I marked it with a blue arrow

[ozzy_sv]

On the salt beach, as well as on wet marshy soil, you have to turn on the beach mode.
Otherwise, the detector simply does not perform a balance on the ground.
At the same time, the depth is immediately significantly lost and all the black metals are masked automatically
If it also happens in the nokta impact - then this is sadness

[Skippy]

Thanks for the larger schematic.

U21 (5V regulator) seems to serve no purpose ? Does it power some of the digital circuitry, like the microcontroller, LCD display ?

It's interesting to see that the coil has different specifications to the Tek T2 (and F75 ), there was widespread speculation that the Racer was a 'copy' of these machines, usually based on the physical similarity, not any real technical assessment. If I were a Makro engineer, I would've be tempted to use a T2 coil (or aftermarket compatible coil) as a development coil, no point re-inventing the wheel.

[ozzy_sv]

Does it power some of the digital circuitry, like the microcontroller, LCD display ?

These parts are powered by the U6 - 3 Volts

U21 (5V regulator) seems to serve no purpose

I, too, was puzzled but there so done
But I did not investigate in detail the digital part, so there may be inaccuracies, since the pcb board has at least 4 layers

[ozzy_sv]

no point re-inventing the wheel.

But it makes sense to sell the same thing again

But in the first different assignment of the pins in the connector, in the second the distance between the fixing ears is also different, from the memory t2 - 18 mm , makro 22 mm

[Skippy]

What I was meant was: use a T2 coil for development purposes, so you're not developing a coil AND a detector, you can independantly produce your own-brand 'Makro-Styled' coil housing with whatever ear spacing you prefer. Coil connectors are easily swapped. Though I've not seen a Racer coil, it's connector couldn't be much worse than the cheapo thing used by Tek/Fisher, so that's one feature to NOT copy. And lower stems/clevis hardware are easily hacked/improvised for testing purposes.

I imagine that would be one of the tricky engineering aspects of the Impact - making the coil work well. I wonder if they kept a centre-tapped TX winding?

[ozzy_sv]

I wonder if they kept a centre-tapped TX winding?

If I understood you correctly then yes
Halves are equal, but there is a small infelicity

[Funfinder]

On the salt beach, as well as on wet marshy soil, you have to turn on the beach mode.
Otherwise, the detector simply does not perform a balance on the ground.
At the same time, the depth is immediately significantly lost and all the black metals are masked automatically
If it also happens in the nokta impact - then this is sadness

Thanks for the Info - this push-trigger ahead and do ground-balance thing was already
from the beginning a little bit tricky.
But we see that the Makro Racer form 2015 made the difference and meanwhile
we have with the Impact the 3rd improved version of it.

The question now is how to implement cavity detection and get more depth by higher coil voltage
or stronger EM-field if this is possible at all.
Additional features like different vibration patterns and inbuilt microSD Card slot plus
wireless mp3-player would be also cool. And of course a lightweight 70cm coil, too!

[Davor]

Sadly, they still use phase shifters to do what code can do better.
At least it seem they did not over-filter baseband signal.

[Math]

heres link to F75 schematic http://md-hunter.com/fisher-f75-circ...-board-layout/

does anyone have Teknetics T2 schematic?

[Math]

on the makro and the f75 whats the purpose of the capacitor/resistor combinations to ground on the rx input before the preamp?