Broxie

Microphone for Laptop

The Covid 19 Pandemic has given me reason to use various video and audio type conference applications in order to access training and social gatherings.

Although my Laptop Computer has these built in, I don’y actually use my laptop as a laptop. It sits up on end with the lid closed. Connected to it is a monitor a USB keyboard, Cordless USB mouse, and an Ethernet cable. It is a close to being a Tower as a laptop gets.

Until the first online meeting I had not even given it a second thought. I joined the meeting relying on the built in microphone. This microphone I had to virtually shout at for the gathering to be able to here me.

The group wanted to see each other and so I figured I would hook up a new unopened albeit several years old Web Camera that has a built in Microphone. That solved the video issue, but being mounted atop a large monitor several feet away, I still found I have to raise my voice to be heard clearly.

If I moved the Webcam closer to me the mic was fine, but then the video was too close in for me and I did not really have anywhere to mount it.

I ordered a couple of cheap vintage style microphones from “AliExpress”.

So while waiting for them to arrive I raided my old salvaged parts bin and set about rigging up an Electret microphone to the Dell Inspirations Headset port.

I do not have one of the TRRS plugs to test the voltages on the Dells socket. I did have a TRS one though as found on standard old style earphones. The output is only about 2 volts using that plug.

Looking around the internet I noted that a Bias resistor and a coupling capacitor are recommended. The resistance apparently between 1K and 22K Ohms. The Capacitor between 1uF and 22uF.

I was getting better results directly attaching the Electret without either of these components.

I tried all sorts of combinations and even tried paralleling a couple of Electrets. Nothing was much better then the Webcams Microphone when more then a few inches away.

My attempts at amplifying them proved useless using the 2V bias voltage available. I might build a little battery powered microphone amplifier at some point.

It occurred to me that I had a Microphone on a little Arduino board delivered recently. I hooked that up and the signal was much improved. At first I thought the on-board microchip was giving amplification. I sourced the datasheet to see if I could employ the same technique.

looking at the circuit diagram the analogue signal simply went through a 150R resistor!

One of the cheap microphones arrived. The signal was again not a lot better then the Webcam Microphone. However, I could now move the Microphone around the desk.

Opening the Vintage Style microphone which has a little switch to enable or disable it. I noted it had an Electret that looked very much like the one from the Arduino. I tried paralleling them but the best output was still from the Arduino’s Microphone Module.

I took a look and they had different part numbers. The Arduino Microphone “CZN-15E” a search suggests these specifications “Microphone 2 feet 50~60DB The sensitivity of 54 “.

The Vintage Style Microphone is just marked SG. These seem to come in various sensitivities . The nearest I fond on a search of AliExpress was this “6050 Microphone capacitance electret SG electret microphone 6050p/9767p pin 9767 microphone pickup”.

For now the two microphones have swapped laces. The higher sensitivity is now installed in the Vintage Style Microphone where it seems to work well. I will test it next time I have to do the video conference thing.

I might order a selection of Electrets from AliExpress to compare at a later date.

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Air Pump Repair and Upgrade

My cheapo air pump failed. I had thought to replace it with something one that lets you set the desired pressure and auto stops when the desired pressure is met.

That automatic type also often have the benefit of a back lit display, which would be handy in the underground parking area, which is where I normally where I use the air pump.

The cheapo pump does not have any illumination and I normally have to use the touch output of my mobile phone to see the pressure gauge.

The pump also lacks a switch, so when the pressure is about right I have to lean in through the car to disconnect it from the power socket.

The UK remains in lock down so a trip to buy a pump when I could possibly repair the existing one seemed wrong.

The repair itself was simple. It turned out the ground wire had broken off inside the 12 volt connector. There was zero strain relief inside the connector, so I added a cable tie and a little superglue to make a strain relief.

If I was still going to use this pump then I wanted to fit some kind of light. I figured I would us a white led of some kind. I was looking around for the best place to mount it and noted what looked like a 5mm led mounting. I assume that the pump might have a lit and unlit option.

The other feature I wanted to add was a switch of some kind. I salvaged a rocker switch with 5 amp at 120 volt contacts on it from a dead piece of electronics. I had to cut out a suitable hole the press mounted switch. The current offload is around 4.5 amps, so I think it will be okay but it could fail.

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Blue Ring Tester

This tester was ordered in error, however it will come in handy to verify transformers and other instructors. It matches the ESR tester I bought at the same time.



I bought it as a kit. Assembly was straight forward and I modified the output section to give banana plug or terminal post fixings for the test leads, just as I did with the ESR meter.

Again I kept the blank end plate in case I modify the outputs to more streamlined flush fitting banana jacks at a later date.

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Function Generator Repair

Several years ago now I purchased a cheap open PCB style “Function Generator”. Even though it was cheap it seemed more logical then building one from scratch. I remember doing that way back when I was in my early 20’s!

More recently I have been attempting to repair a Hameg 203-6 and the only safe signal to had was the units calibrated square wave. As the Oscilloscope appears to be modulating it would have been nice to have a separate wave form generator. I do have another Hameg but space on my desk is limited.

I recalled having this function generator but suspected I had chucked it in the spare parts bin when it failed.

I fished it out and supplied it with 6V. This value was chosen as I spotted it has a 78L05. The LCD proved to be faulty as did the main PCB.



I have another LCD that will do the job on order form “Aliexpress” but that could be months arriving. So I disassembled the LCD cleaned the tracks with some isopropyl alcohol and reassembled the display. This reassembly proved quite difficult, but I did eventually get a usable LCD.

Pocking around with a meter and a scope seemed to indicate that the microprocessor was still working. The LCD confirmed that it was at least talking to that.

There are 2 other IC’s on th PCB. The first is a surface mount dual low noise op amp (NE5532) and the other is a socket mounted thru-hole super voltage converter (ICL7660S). It was far more likely that the voltage converter was faulty and possibly even expected to fail, if the socket mount was anything to go by.



As the parts were coming from China, I ordered a quantity of each. They arrived in due course and I slotted in the ICL7660S to restore operation.

I still do not have a dedicated power supply or a case for this unit so it might become a project to make it into a bench instrument as I have a supply of spares should I blow it up!

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Bob Parker Blue ESR Tester

My options for testing capacitors are quite limited, up till now my choices were to place a multi-meter on ohms range across them and look to see how fast or slow they charge and discharge over a give range or to desolder them and try and test on the capacitance range on a old multi-meter that has a transistor tester, frequency counter and capacitance checker.

Watching a repair video from one of my favourite YouTube channels “EEVBlog” . Dave Jones was using a older style Bob Parker ESR tester that seemed to do a good job of identifying faulty capacitors. This unit is not available though some that performed a similar task were on offer from all the usual places.

Digging around a bit more I located a seller in the USA selling the latest version of the Bob Parker ESR tester as well as a matching “Ring Tester for High Q Inductive Components” by “AnaTek”.



Both of these Items were available built or in kit form. I decided to buy the kit form.

I was going to just order the Capacitor Checker. At the point of ordering I selected the wrong item! Realising my error I ordered the more expensive Capacitance Tester as well from the same supplier.

Both of these Items were available built or in kit form. I decided to buy the kit form.

Resistors in first

I was going to just order the Capacitor Checker. At the point of ordering I selected the wrong item! Realising my error I ordered the more expensive Capacitance Tester as well from the same supplier.

The case that comes with these is interesting and a has a battery compartment that can take 2 AA cells using the provided spring clip fixings or as in these meters a single PP3.

Each case came with a spare blank end as well as the one with holes for the AnaTek meters on/off switch and test leads. Two grommets were supplied to pass the supplied cable through.

I dislike that feature, so I utilised some cheap terminal posts I have laying around from a past project. These I had to mount in a odd fashion but they work well.

I may get some more modern banana plugs sockets at a later date. They would need mounting in a different location so I have kept the spare end plate just in case.

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Joule Theif V1

Long ago when I was first starting out with electronics and buying magazines like “Every Day Electronics”, “Practical Electronics” and “Electronics Today”, I read an article about a “Joule Thief”. I never did build the project, but the name stuck with me.

More recently I was watching one of my favourite YouTube Channels “Big Clive”. Clive was talking about the “Joule Thief” circuit. I decided to see if I had enough parts laying around to make one.

My biggest issue was a lack of transformers or instructors. I did eventually find a suitable looking transformer on a old PCB.

Using that was not successful at first. Doing a little research on the internet I noted that someone who had a low turns ratio had manage to get there circuit working with a capacitor.

I reached for my odd capacitor box and with a bit of trial and error I found a few values that made my circuit work. I settled with a 4n7 as that gave the brightest glow from my test LED.

Later I decided to push the circuit and apparelled 2 red and a green LED.

Broxie Cad Joule Thief
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Hameg 203-6 Day 4

I assembled much of the front panel and tinkered around. I seem only to be able to get a trace under certain conditions. Although I now have a shape trace it is rolling and seems to be modulated. I know all the switches and potentiometers are dirty. this is adding to the confusion. So, I have packed the oscilloscope away for now.



When I have some switch cleaner and some more time I will try again. I would also like some way to test the old capacitors. I am thinking I may have to get the PCB out of the chassis to be able to access some components.

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Hameg 203-6 Day 3

My attention turned to the intensity and focus of the trace. looking at the circuit diagram and searching around the internet for ideas. I read some place that the high tension resistor chain is prone to have resistors going high or open circuit. Following up on this I found I did indeed have a resistor that had gone high in value.

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Hameg 203-6 Day 2

Having manage to get a faint blurred trace on my previous attempt at fixing this oscilloscope I figured on trying to increase the displays intensity and focus.

However I found even the faint trace to be very intermittent. I tentatively measured the heater voltage and it was getting the required voltage. The voltage rails on the oscilloscope are huge and would blow my cheap old multi-meter apart in an instant. I was shapely reminded of that when I slipped and gave a finger a quite zap, with a audible crack as something discharged into it.

With the power off I closely examined the PCB around the area of the CRT outputs, and I discovered what I believe to be the original fault. It looked to have been a manufacturing fault. A link wire that had been slightly bent over had missed the flow of the solder completely. Occasionally making enough contact with the bare copper pad and thus working from time to time. This is the most likely why the selector had been abused, trying to get a trace.

I had to solder it as best I could as I have not yet managed to find a way to remove this PCB without removing the transformer wiring.

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Hameg 203-6 Day 1

Long ago I bought 2 Hameg 20mhz Oscillosopes from eBay, most likely as a job lot spares or repairs, in the hope that I might make one good one out of the pair.

As it turned out they were not identical the other one is a slightly newer model 203-7. Fortunately that one does work, not perfectly but has been usable enough for my needs.

Both items have been sat in storage for years now, but my new found interest in my old hobby and profession necessitated my seeking them out and using on my multipurpose computer desk come work bench.

The 203-6 had never worked since the day I got it. As it is sitting there I recently decided to see if I could find the problem. Or more accurately problems.

The first was it had no trace at all and the trigger selector switch was sticky and had been poorly gummed in place by someone trying to repair it. I disassembled the and cleaned off the “hot snot” that had been applied.

The multi position selector had been abused and all the little notches were jamming. This must have been the case for some time and was the likely cause of the connecting support for the chassis being snapped. Hence the “hot snot” which looked to have been squirted in from the side without disassembly.



This did not completely restore operation but at the end of a long evening I did have a faint and very blurred trace.

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