dsPIC Audio Filter (Part 1) by Leon Heller G1HSM

I designed this simple unit a couple of years ago, when the Microchip dsPICs first became available. The dsPICs are described as digital signal controllers by Microchip, that is, micro-controllers with additional digital signal processing capability, as opposed to pure digital signal processors (DSPs) like those produced by Texas Instruments and Analog Devices. Unlike conventional DSPs, the dsPICs are quite easy to use from a hardware point of view, as many of them are available in user-friendly DIL packages.

The article is in two parts, a brief introduction to DSP and a description of the hardware, to be followed by a description of software development.

DSP applications like this are conceptually quite simple, the audio input is sampled using an analogue to digital converter (ADC), which converts the signal into numerical values. The numerical data are then manipulated by the DSP in some way, such as applying a filtering algorithm, and then converted back into audio using a digital to analogue converter (DAC). Sampling has to be done at a frequency that is at least twice that of the bandwidth of the signal, and it is usual to  filter the signal before the analogue to digital conversion to avoid ‘aliasing’, that is, signals outside the required band getting converted and mixed up with the required signals. Once this has happened they cannot be removed. For many applications such as this, the ADC,  DAC, filters and pre-amplifier are often combined in a single device called a codec (coder-decoder).

The schematic should be fairly self-explanatory to anyone who has some micro-controller experience. I used the 40 pin DIL version of the dsPIC30F4013 which is a 5V device, with the Si3000 audio codec. The codec is designed for speech systems, and is easily interfaced to the dsPIC. It contains a headphone amplifier as well as the pre-amplifier. I’ve provided a microphone input (an electret microphone works very well) and outputs to stereo headphones as well as  line input and output.

Although I’m not using them in this application, I’ve included a potentiometer which may be read using an ADC input, an LED and a push-button. These may be used for functions like menu selection, digital volume control, and debugging.
The PCB is single-sided, and I made the prototype at home. The Si3000 is only available in a SOIC (surface mount) package, and is therefore mounted on the underside of the board. The grey connector is for the Microchip ICD 2 programmer/debugger. This is quite an expensive unit, and I could provide programmed chips to anyone who wishes to build one of these units. I had a small batch of the boards made in the Far East, they weren’t very expensive.

Software development will be covered in Part 2.

Leon Heller, G1HSM June 2007.

Return to the index of Vital Spark articles.

G3MGQ’s Month on the Air

Prepared by the clubs RSGB trainer, G3MGQ, you will find the latest DX contests including the ones to shoot for as well as ones to give a wide berth. Why not download the latest edition of Month on the Air and enjoy your DX just that little bit more.

Become a member of HERC

Join the Hastings Electronics and Radio Club.

Why not join one of the largest and most established Radio clubs in the South East of England? Very low joining cost, and free for a year to new licencees.

Vital Spark Archive

Vital Spark newsletter articles

Take a look through a large selection of articles written by club members over the years which have been published in the monthly Vital Spark newsletter .

Used Ham Radio Equipment

View HERC's Used Ham Radio Equipment for sale list..

Every four weeks, HERC's Used Ham Radio Equipment for sale list is updated on the site. Bookmark the gear for sale page to re-visit easily and take advantage of the used equipment on sale through the club.

Club Photographs

HERC Image Galleries.

Here is the official HERC photograph archive which contains multiple image galleries spanning several decades since the club was formed many years ago. Enjoy the images!

UK Amateur Radio Repeaters

UK repeaters

Click button above for full list, or a local repeater callsign below for info.

GB3EB 2m in Uckfield- Active
MB6EB 2m DStar Node in Eastbourne - Active
MB6RY Wires-X DigiGate in Broad Oak - Active
GB3HE 70cm in Hastings - Active
GB7HE 70cm DStar in Hastings - Coming soon
GB3ZX 70cm in Eastbourne - Low Power
GB3JT 23cm ATV in Hastings - NoV cleared
GB7RY 70cm X-Wires Repeater Rye - Active
GB7ES Eastbourne - DSTAR Rpt. - Active
GB3ES 2m in Hastings - Active

For a complete list of repeaters, head over to
the UK Amateur Radio repeaters list.

Popular pages

Get your amateur radio licence - Find out more about amateur radio licence training.
Month on the Air - G3MGQ's popular monthly DX contest/expedition list.
Wilf Gaye Memorial Cup - The clubs annual operating event in the memory of Wilf Gaye M0GYE.
St. Richard's College Buildathon/STEM/ARISS - HERC attends St. Richard's Catholic College for their various events surrounding the Tim Peake ARISS contact.
G3BDQ - John Hey's Rare QSL Cards.
Sussex Electronics Radio Fair - SERF Sussex Electronics Radio Fair 2016.
Vital Spark - A selection of articles re-published from the Vital Spark.
RSGB News - Find out how to get RSGB news on your mobile or PC.
Experimenters Corner - A selection of Proteus projects by Bob Gornal (G7DME)
BBADL - Bath Based Distance Learning Course.
Conquest Hospital Radio - Presented by HERC member Antony (G4CUS).
Radio Rallies 2016 - An up to date list of radio rallies scheduled for 2016.
Club QSL Cards - A selection of QSL cards the club has received over the years.
Other Newsletters - Excellent newsletters and magazines from other clubs.
TX Factor episodes - Take a look at the TX Factors YouTube videos.
John Taplin - A bio of the late John Taplin.

Amateur Radio Resources

Other Radio Clubs & RAYNET

BSARS - Brede Steam Amateur Radio Society

RAYNET - The Hastings and Rother RAYNET Group.

HERC members sites

Sigord - Gordon Sweet
Hastings Radio Comms - Andrew Haas-Campbell
Hoofbags - Liz Costa

Categories