Urban Ministry Live And Unplugged: BFO Metal Detector [2]

Wednesday, May 21, 2008

BFO Metal Detector [2]

Here are instructions for the search coil of the metal detector above. It requires 70 turns of 30 swg (22 awg) enamelled copper wire on a 120 mm (4¾") diameter former. Neither the winding of the coil nor the wire gauge are critical. Wind the coil around the former, and temporarily hold it together with stubs of insulating tape. Then bind it tightly with insulating tape all round. Scrape the enamel off the ends of the coil's enamelled copper wires. Then add a Faraday electrostatic shield, for stability. Prepare some long, thin strips of tin foil. Twist a 100 mm (4") length of bare wire around the coil, over the insulating tape. This provides electrical contact with the foil. Now wind the foil around the circumference of the coil -- beginning at the base of the bare wire -- yet the foil should not quite complete a full 360°. Leave a small gap as shown. Now tightly bind the whole Faraday shield with insulating tape. Attach the coil to IC1 by means of microphone cable, with the cable's screen(s) going to the Faraday shield at the one end, and to -6V (negative) at the other. The coil may be mounted on a rigid plate, and a suitable handle attached. OBSERVATION: Click on the diagram to blow it up. You could wire the coil directly to the circuit if you're in a hurry.

NOTE: You may re-publish this design, on condition that you acknowledge the designer (Thomas Scarborough) and this blog (http://thomasscarborough.blogspot.com).

4 comments:

Anonymous said...: U r a nice man. Thank u.; August 12, 2016 at 10:36 AM
metal detector Philippines said...: I lost my ring in a volleyball court & came across Metal Detectors site. Like everyone has said here, money well spent and saved me really! I was very appreciative of all of the helpful advice on how to use it. He was very nice & helped us find my rind and it was quick... Highly recommended!; November 9, 2016 at 2:25 PM
Unknown said...: Can i use alluminium foil from broken down capacitor for faraday shield ?; July 9, 2017 at 6:59 PM
Thomas O. Scarborough said...: Yes. So long as the foil conducts from beginning to end. There should not be an electrical break, except for the gap in the Faraday shield.; July 11, 2017 at 7:55 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.