The design of the universal body of the metal detector. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / metal detectors
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In amateur radio literature, many successful designs of various cases for electronic devices are described. Not all of them are suitable for autonomous battery-powered devices, which include metal detectors. A number of requirements are put forward for the body of a metal detector: compactness, strength, reliable fastening of printed circuit boards and batteries, and convenience of work in field conditions. There are also specific requirements, such as the presence of low-resistance and time-stable contact between the massive metal parts of the case.
Below is a description of the design of a universal housing suitable for accommodating the "electronic stuffing" of almost any metal detector of medium complexity. This housing is suitable for all metal detector circuits described in the book. The author sought to create a manufacturable and easy-to-manufacture hull design that meets all of the above requirements. On fig. 41 shows a general view of the universal case developed by the author.
Rice. 41. The design of the universal body
The body consists of two sidewalls 1 and 2, which are made of aluminum alloy sheet 4 mm thick. In the sidewalls there are holes with M3 thread for mounting screws, with which the rest of the body is attached. On the sidewall 2 there is also a connector 9 for connecting the sensor cable of the device. On the inner side of the sidewall 2 there is a contact tab of the device housing, through which a common bus of the electronic part and cable screens are connected to it. This lobe is clamped under the nut of one of the connector fastening screws 9. The metal of the sidewall under the contact lobe is carefully cleaned. To ensure stable operation, no other contacts of the device housing with a common bus of the electronic part are allowed!
On the front panel 3 (shown on the example of an induction metal detector) there are pointer devices, balancing potentiometers, an operating mode switch and a piezoelectric emitter (on the inside). The front panel is two-layer. The outer layer - false panel is made of black anodized aluminum sheet 0,5 mm thick. The necessary lines and inscriptions are engraved on it. The panel itself, located under the false panel, is made of sheet fiberglass with a thickness of 2,5 mm.
The rear panel 4 is easily removable and serves as a cover for the battery compartment. It is fastened with one screw to a threaded bushing fixed on the partition 5. In order to prevent the rear panel from bending when its only fixing screw is tightened, it is reinforced with a profile in the form of a wide channel, bent in the same way as the panel, from a 1 mm thick aluminum alloy sheet. The profile and the panel are fastened with four M3 screws with nuts.
Top cover 6 and bottom cover 7 are the main protective elements of the case. Covers are made of sheet aluminum alloy 1 mm thick. The lids are identical in shape and are 100% mirror images of each other.
The printed circuit board 8 of the electronic part of the device is attached to the end surfaces of the sidewalls 1 and 2 using screws screwed into the threaded holes of the sidewalls. The printed circuit board is installed with parts inside the case and there is a sufficient gap between it and the top cover 7. To modify the induction metal detector and for more complex devices, threaded holes are provided in the lower end surfaces of the sidewalls 1 and 2 for installing an additional printed circuit board. It is installed parallel to the main printed circuit board 8 also with parts inside the case. Details on printed circuit boards are placed so as not to take up space at the locations of pointer microammeters and balancing potentiometers.
M3x6 screws for connecting individual parts of the case were used from a set of fasteners for assembling computers. They have a reliable and beautiful chrome-plated coating and a cross-sectional shape slightly different from a circle (i.e., they are a kind of self-tapping screws), which provides a strong fastening that does not unscrew from shock and vibration and (!) Reliable electrical contact.
It is desirable to subject all aluminum parts of the case to electrochemical treatment (anodizing in chromium peak), which will give them not only an attractive greenish tint, but also protect them from corrosion. Despite a significant oxide layer on the surface of anodized aluminum, the contact between the metal parts of the case remains reliable and stable. This is achieved by using special screws (see above), tightened with sufficient force into the threaded holes of the sidewalls (without oxide) and in contact with the inner surfaces of the holes of the parts (also without oxide - drilled).
Author: Shchedrin A.I.
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