The following information is intended to help PICAXE users to get their SOMO 14D audio/sound modules working with a PICAXE microcontroller.
The 4D Systems SOMO 14D audio/Sound module is a small (~19mm x ~21mm) 14 pin drop-in module that can play back audio files stored on a micro SD memory card. The module supports 4-bit ADPCM audio files (.ad4 filename extension) with sample rates from 12Khz up to 32Khz
The SOMO 14D module has two modes of operation, SERIAL and KEY.
The Serial modules utilises an SPI type interface with two or three wires under the control of a separate microcontroller such as the PICAXE. The key mode allows stand alone operation without a host control device using three push button switches.
This post predominantly addresses the SERIAL mode of control using a PICAXE controller.
While two wire control is possible, if playing longer audio files and wishing to ensure that they are played to completion before starting to play a new file, then it will be necessary to use a third wire to monitor for completion of playback of a prior audio file.
Additionally some may wish to implement a hardwired RESET between the PICAXE and the SOMO module as discussed below.
Audio output can be derived using a speaker (8/16/32 Ohms suggested) connected directly across two pins of the SOMO 14D module or alternatively an audio output pin is provided for connection into an amplifier if desired.
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A few points of caution and information:
1. Power Supply:
While the SOMO 14D datasheet indicates that the module will operate from a single power supply in the range 2.7Vdc to 3.6Vdc, a few users have found that operation below 3.0/3.1Vdc may not be reliable.
Operation from a well regulated 3.3V power supply is recommended (eg a LP2950-33 as a 3.3V 100mA supply). The datasheet indicates the power consumption at 3.3V supply as 10uA typical at idle and a max of 45mA when playing an audio file).
I forced a voltage dip (by connecting a 220uF capacitor) to the power supply while the SOMO 14D was operating which caused the SOMO 14D to immediately change to playing another audio file.
Conclusion is that while I personally have operated a SOMO 14D module with only a 4.7uF electro type capacitor between the voltage regulator and SOMO module, the addition of the recommended electro capacitor is in the range 100uF to 470uF at/near the SOMO 14D terminals should be done.
If the environment is electrically noisy, it can also be useful to install a 100nF ceramic or mono type decoupling capacitor across the power supply close to the SOMO 14D module to help filter out switching disturbances.
2. uSD Memory Cards:
There have been problems with various makes of micro SD memory cards. Not all cards work well. A good sign of memory card problems is if you are having problems playing all songs, the SOMO 14D module “jumps” to another song before completing the previous song, the volume level changes for no apparent reason, or you hear pops/clicks particularly when using a speaker directly connected to the SPK terminals.
4D Systems has indicated that correct operation with:
- a Sandisk 2GB uSD card, . . . . . . . I (westaust55) have used a Sandisk 2GB uSD card without problems
- a Kingston 1GB uSD card . . . . . . . . . Grogster has reported success on this forum with a Kingston 1GB uSD card
uSD cards as found to work by others:
- a DSE 2GB uSD cards from Dick Smith Electronics in Australia (reported by WestAust55)
- an A-Data 2GB uSD card, (reported by Grogster)
- a Transcend 2GB uSD card (reported by Grogster)
- a Fujifilm 2GB uSDcard (reported by picIt)
- a Kingmax 256MB uSDcard (reported by goom)
- Kingston 2GB uSD card ( two examples tested and working by Westaust on 14Dec09).
These Kingston cards have the number 6603363B on the bottom right at rear of the retail packaging card. See attached image
The following cards are known to give problems (this is far from a complete list):
- Kingsmax – 64MB (reported by westaust55)
- Lexar 2GB (reported by westaust55)
- SanDisk 1.0GB (reported by goom)
- Kingston 2GB (reported by goom and Grogster) – seems 1GB cards work but both members had problems with the 2GB version
.. Goom reported that the Kingston 2GB that does not work has 6602523B on the bottom right of the rear of the retail package.
- Apacer 2GB uSD card (reported by Grogster)
(let me know by PM of any others you have success or failure with and I can add them to this post to keep the list as comprehensive as possible)
The uSD card MUST be formatted using the FAT/FAT16 format.
4D Systems recommend that when used with the SOMO 14D module, rather than just adding additional audio files to the uSD card, that the card be re-formatted and all required audio files be added at one time.
3. Direct Speaker Connection:
The datasheet (up to Rev 3) indicates that a speaker of 8, 16 or 32 Ohm 0.25W rating can be connected.
However, in a response to a post on the 4D systems forum, the 4D Systems technical people made the comment:
“Speaker: 8 ohm 1W (Not recommended), 16 ohm 0.5W, 32 ohm 0.25W”
While the 8 Ohm speaker is apparently not recommended, I have been using a higher quality 8 Ohm 3 Watt speaker without signs of any problems.
4.Using the SOMO Audio Output Pin (pin14):
Some users of the SOMO 14D module have reported audible click sounds between playback of files.
Seemingly this applies in the KEY mode operation resulting in a noticeable click when there is no sound file playing and you click Next, Previous or Play. As at Rev 3 of the datasheet, a transistor based switching circuit driven by the BUSY signal is now recommended by 4D systems to disable the audio line between playback of files.
The data sheet shows using a .1uF capacitor in series with the audio out pin (pin 14). Some users have indicated that this seriously reduced the bass response. A recommendation has been to use 2.2 uF bipolar electrolytic instead.
5. Audio File conversion:
Audio file names do not need to be in sequence. There can be gaps in the file name numbering.
Some users reported that converting their mp3 and .wav files to ad4 format resulted in pops and clicks being heard during playback with the SOMO module. The same users indicated that selecting the sample rate for conversion to ad4 equal to the original mp3/wav file sample rate resulted in playback without pops and clicks.
Sometimes when you convert the mp3/wav file to an ad4 file it becomes corrupted if you try to change the data rate. This can give the impression of clicks. Try converting the file back to the original format and see if it still sounds OK.
6. Operating with the PICAXE at 5Vdc
If you are powering your PICAXE at 5Vdc, then as per the datasheet, you need to include series resistors in the Clock and Data lines between the PICAXE and SOMO 14D module.
The datasheet indicates 470 Ohm resistors as adequate. I have used 1.2k Ohm and 4.7k Ohm resistors without disrupting control of the SOMO module.
There is no need for a resistor in the BUSY signal line from the SOMO 14D module to the PICAXE. In fact, adding a resistor of a relatively high value may cause problems.
7. PICAXE to SOME 14D circuits - some further recommendations:
If you are having problems getting your SOME 14D audio module to work correctly, here are some further recommendations
- Add a 100n cap across the PICAXE(as close as possible) to filter out PSU noise
- Add a 220uF or 470uF/16v cap across SOMO supply, as close to module as possible
- Add a 100n cap across SOMO supply, in parallel with the electro capacitor
- try wiring a RESET line control from the PICAXE – so the SOMO is reset before selecting any audio file.
- Do not include diagnostic LED's on CLK, DTA and RESET lines (but keep the 330R series resistors)
- if you have an LED connected to the SOMO 14D busy line, try removing that play indicator.