Silicon Chip – May 2019

siliconchip.com.au Australia’s electronics magazine May 2019 107

Hanson, although many other suppli-
ers can order the Clipsal parts, eg, John
R. Turk. Look up “electrical wholesaler
near me” online.

Converting LPs to MP3s

I would like to copy my LPs to a
USB memory stick to listen to in my
car. Can I connect my turntable to an
analog-to-digital converter board fed
into a USB socket to achieve this? Is
an intermediate amplifier needed, be-
tween the turntable and the analog in-
put? Could an Arduino Mega be used?
(M. P., Croydon, Vic)

• You need an RIAA preamplifier to
  boost the low-level signal from the
  magnetic cartridge on the turntable up
  to line level, and also to provide the
  correct equalisation. Otherwise, the
  result will sound wrong. You can then
  feed the output of the RIAA pream-
  plifier into a computer for recording.
  We published an article on how to
  do this in the September 2006 issue,
  called “Transferring Your LPs to CDs
  & MP3s” – see siliconchip.com.au/
  Article/2769
  Our latest RIAA preamplifier design
  was published in the August 2006 is-
  sue. The article was titled “Build A
  Magnetic Cartridge Preamplifier”
  (siliconchip.com.au/Article/2740)
  and a kit for that project is still avail-
  able from Altronics (Cat K5513). We
  also sell the PCB for that project in

our Online Shop (siliconchip.com.au/

Shop/8/860).

Once you have a suitable RIAA

preamplifier connected between the

output of your record player and au-

dio input on your computer, you can

use free software such as Audacity

(www.audacityteam.org/download/)

to record the audio.

To save the result in MP3 format,

you also need an encoder called

LAME, which interfaces with Au-

dacity and can be downloaded from:

https://sourceforge.net/projects/lame/

Trouble getting banana

plug sockets

I notice that the PCB-mounting ba-

nana sockets used in the Wide-range

Digital LC Meter project (June 2018;

siliconchip.com.au/Article/11099) –

specified as Altronics Cat P9200 &

P9201 – are no longer listed on the

Altronics website or in their latest

catalog.

Can element14 Cat 1698982 be used

instead? I’d welcome other alterna-

tives. (S. E., Scullin, ACT)

• It is unfortunate that these parts
  have been discontinued not long af-
  ter we’ve used them in a few differ-
  ent projects.
  The dimensions of the part that ele-
  ment14 sells look similar to the ones
  we used but not identical (for example
  the pins are 1.3mm vs 1.2mm wide),

but we think they will probably fit on

the PCB and do the job, even if they

are not a perfect match.

Another reader pointed out these

sockets from eBay; again it is hard to

be certain that they are an exact match,

but they will probably be close enough:

http://www.ebay.com.au/itm//152700921462

We will try to find a source of these

parts so we can sell them in our On-

line Shop, to make it easier for read-

ers to build this project.

Different relay versions

causing problems

I just built the Wide-range Digital LC

Meter (June 2018; siliconchip.com.au/

Article/11099). The build was straight

forward, and when I powered it up, I

was greeted with the initial screen dis-

playing the values of L and C. I could

connect to it using my laptop and ad-

just the parameters.

I tried measuring a 10μF capacitor

but the test frequency only read 0Hz

or 10Hz. I used my DMM to check for

driving signal for the relays on the Ar-

duino digital outputs at D6 to D9, but

I only read just over 1V; not enough

to trigger the relays.

I decided to de-solder one relay and

the reading on that driving pin was

then 5V. I concluded something was

wrong, so I desoldered the three oth-

er relays, and discovered they would

only switch on if the power was ap-

As the owner of a vehicle with the

unswitched auxiliary power outlet

‘feature’, I’d like to say what a pleas-

ant surprise the Motion-Sensing 12V

Power Switch project was in the Feb-

ruary 2019 issue (siliconchip.com.

au/Article/11410). I have already or-

dered a short form kit of parts.

I had been contemplating building

an automatic switch myself and had

gone through similar thought pro-

cesses as Nicholas Vinen but had not

turned it into reality. What modern

manufacturers are thinking when

designing car electrical systems is

sometimes a mystery.

In addition to the unswitched

power outlets, my vehicle’s exte-

rior sidelights come on whenever

a door is opened; it does not matter

if the light switch is on or off. I’ve

lost count of the number of helpful

bystanders who point out I have my

lights on when loading the car at the

supermarket. I then have to explain

that this a feature of the car and not

me being forgetful.

One thing not covered in the arti-

cle is the maximum current allowed

through the circuit. I plan to connect

a dashcam, navigation device and

transceiver with a current draw of

12A on transmit for say a total of 15A

maximum. The IRF4905 appears to

be rated at 50A, providing the wir-

ing can take the load, should it be

OK? Keep up the great work. (N. D.,

Ocean Beach, WA)

• Thanks for the feedback. Some-
  times manufacturers do not think
  through the ramifications of doing
  things in an unusual way.

Current rating of 12V Motion-Sensing Power Switch

Practically speaking, the device

as presented should be good for

around 5-7A. While the IRF4905 is

rated higher than that, it would need

heatsinking. Even at 7A, the TO-220

package would get pretty hot. The

SMD version should not be used in

situations where the current draw

would exceed 5A.

There are alternative Mosfets

which could handle up to 15A with-

out heatsinking. You would need

one with an on-resistance of 4mW or

less. For example, these should all be

suitable: AOT240L, CSD18511KCS,

IRFB7437PBF, IRFB7446PBF.

As you say, the wiring would need

to handle this current to, as well as

the plug and its integrated fuse (and

make sure to solder those wires close

to the Mosfet leads).