Urban Ministry Live And Unplugged: BB Metal Detector (556)

Thursday, June 27, 2013

BB Metal Detector (556)

It's been a while since I've shown one of my electronics designs here. This one is Copyright © Thomas O. Scarborough, but feel free to copy it with acknowledgement (click on the image to enlarge). This is a self-contained Beat Balance (BB) metal detector. It is not the same as Induction Balance (IB). As will be seen, the concept lends itself to extreme simplicity. It also offers considerably better performance than Beat Frequency Operation (BFO) -- in this case about twice the sensitivity. This is I think my best design for simplicity and sensitivity combined (see BB Metal Detector for an even simpler design and a few tips on construction). Details of the coils are at BFO Metal Detector [2]. Place the coils for greatest sensitivity -- some patient experimentation will be required. VR1 may be a multi-turn potentiometer for more precise control. The "mirror" design ensures good stability. Note that this 556 is a CMOS device (e.g. the 7556), not the bipolar device.

4 comments:

Unknown said...: i have one question, maybe its stupid but i am new to this, what is work voltage on capacitors?; January 9, 2015 at 6:36 PM
Thomas O. Scarborough said...: The capacitor voltage: typically this is anything above the supply voltage. So if the supply voltage is 12V, the capacitor may be, say, 16V or 25V. In this design, you ideally need a non-polar capacitor. This can also be made of polar capacitors in series, wiring the negative terminals together.; January 9, 2015 at 7:22 PM
Anonymous said...: Will the circuit work on 9 volts? In other words, could a 9V regulator IC be put in pto the 12V circuit, as you have recommended with other circuits?

Also, R & L on the coils correspond, essentially, with the beginning of the winding and the end of the winding, so, to clarify, the coils are wired into the circuit opposite to one another (if that makes sense), am I right?

Thanks!; June 14, 2024 at 6:14 PM
Thomas Scarborough said...: According to the data sheet, you can try 2-18V. 9V is good. That is, for the CMOS 7556. I used the CMOS ICM7556.

About orientation of the coils, any orientation will work, but experiment to see what works best. The coils overlap one another by about one-third.; June 18, 2024 at 5:50 PM

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About This Blog

I have spent ten years in suburban ministry, twenty-two years (total) in urban ministry, and seven years in country ministry. My involvements in ministry continue, now reduced.

There are a few reasons for this blog: 1. To help people form a picture of what ministry is about -- in particular urban ministry -- not least seminary students who may be destined for urban ministry. I have found that the image and the reality may be far apart in academia. 2. My experience in ministry may be (and, in fact, often has been) an encouragement to other ministers -- alternatively, a cautionary tale, as the case may be! Many notes of thanks have been recorded on this blog. And 3. Friends have simply told me how interesting reports of ministry are.

This is not a "parochial" blog. Only a tenth or so of readers are local (in South Africa). Outside of my home country, this blog is most read in Europe and North America. Russia is no. 4 on the list, and there is some interest in Muslim nations. At one point, this was the most authoritative Religion blog in Southern Africa (I now do not know how it is ranked).

With all of the above in mind, the purpose of this blog is simply to record urban ministry "live and unplugged", in the form of accounts. This blog is not a "church blog", but a "ministry blog". For the most part, I don't intend to share my views. The emphasis is the experience of ministry and the various events that surround it.

A definition of “live” is “actually being performed at the time of viewing”. A definition of “unplugged” is “without amplification or modification”. However, see my Posting Policy below.

Posting Policy

This blog may be unique with regard to its degree of transparency about urban ministry. Many people have written to me to say how they cherish the help they have received through this. However, this means that special attention needs to be given to confidentiality in particular. I use the following guidelines for posting on this blog:

I apply the following questions to posts: Are they posted in good faith? Are they balanced? Are they compassionate? Are they informative about ministry? Do they help one better understand a problem or issue?

I consider a post to be unproblematic if a person's identity is unknowable in the post, if the facts are public knowledge, or if a change of particulars (name, place, date, and so on) will truly protect privacy. If I consider that anyone who was not involved in an incident would recognise those who were, then I do not post. If a post could compromise the safety of those I blog about, then I make a post safe, or I do not post.

I believe that these measures should enable me to continue to be "open" about urban ministry while not compromising privacy.

In 2013, ninety percent of the posts on this blog were removed. I then put the question of the freedom of the blog to the South African Human Rights Commission. The position is this: if a post is legal, it is legal. Essentially, all of my posts were OK. There is freedom of expression in South Africa.

Having said this, if any post should even cause discomfort, it will be removed from this blog immediately. This has always been the position. One does need to contact me for that, best through an e-mail or a blog comment, and I prefer to see a name on it. The post will be put back up only if there would seem to be compelling reason for it. It is hoped that there will be the assumption that I wish to address any discomfort satisfactorily, compassionately, and efficiently.