September 2, 2015 – Experimental Engineering

Posted on September 2, 2015 by The Engineer — Leave a comment

Baofeng Battery Capacity Lies

I’ve had a couple of larger batteries for my UV-5Rs for some time now, and decided to do a quick teardown to see if they’re actually the capacity claimed.

Here’s the label, claiming 3800mAh (3.8Ah) of battery capacity.
These batteries are held together with glue, but a good way to get these kinds of things open is by whacking the seams with the handle of a screwdriver. This cracks the glue without damaging the casing.

After a few minutes of cracking the seams, the battery comes right open. The pair of wires link the protection board on the cells to the DC terminals on the top of the pack. The charging terminals are under the cardboard insulator on the right.

Here’s the other half of the case, with the cells themselves. These are wired in series for a 7.2v pack, and at a capacity of 2600mAh (2.6Ah) printed on them, the label clearly lies about the capacity.

Posted on September 2, 2015September 2, 2015 by The Engineer — Leave a comment

Rigol DS1054Z 12v Power Supply Noise Filtering

Since I fitted my scope with a SMPS based 12v input supply, there has been a noise problem on very low volts/div settings, this noise isn’t present on the mains supply, so I can only think it’s coming from the switching frequencies of the various DC-DC modules I’ve used.

Because of this I’ve designed a linear post-regulation stage for the supply, to remove the RFI from the DC rails.
This board takes the outputs from the DC-DC converters, removes all the noise & outputs clean DC onto the mainboard of the scope.

As the scope internally uses regulation to get the voltages lower, I’ve found that I don’t have to match the outputs of the mains supply exactly, for the +/-17.5v rails, 12v is perfectly fine instead.

Here’s the PCB layout, with the 6 common mode filters on the input (left), linear regulator ICs in the centre & the output filters on the right.

Here’s the schematic layout, as usual the Eagle Project files are in the link below, I’ll update when I have built the board & tested!

[download id=”5589″]

73s for now 🙂

Posted on September 2, 2015 by The Engineer — Leave a comment

USB1100 Digital Message Unit

This is basically an industrial, rugged MP3 player, in an extruded aluminium case.
They are used in commercial settings for generating telephone hold music or continual playback of background music in shops.

It’s quite a compact unit, in a nice aluminium case, designed for mounting into a comms setup. This unit will play any MP3 file, up to a maximum size of 11MB.

Here’s the user connections on the end of the unit. The device takes a standard 12v DC input, and has a single button for setup, user feedback is given through the multi-colour LED next to the power jack.
Both 8Ω & 600Ω audio outputs are provided for maximum compatibility. Volume & tone controls are also here.
On the other end of the unit is a single USB port for loading the audio files from a USB drive, and a reset button.

Here’s the single PCB removed from the casing. Unfortunately the main CPU has had it’s part number sanded off, and I can’t be bothered to try & find out what kind of processor it is at this point. To the right of the CPU are some flash ROM & SDRAM, along with the single USB port at bottom right.
The left side of the board is dedicated to audio output & voltage regulation, there are a fair few linear regulators in this unit.

Here’s the audio output side of the board, the transformer on the left is to provide the 600Ω output, the audio amplifier IC (BA5416) is just behind it. To the right are some of the main voltage regulators, a 5v one on the heatsink & a LM317.

The audio codec is a CS4271 from Cirrus Logic, a really high quality part, 24-bit resolution, 192kHz Stereo codec. Considering this is for telephone & PA systems that aren’t that high fidelity, it’s well built!