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October 31, 2011
Product DEV-10342 |
about 2 years ago
Alright, Disregard my last post. I found the problem. This number is not valid for the 4735 variant of this radio. It’s noted in the command/response description in the programming guide.
What I can tell you from my testing is that going up on the value of L1 improves the high end of the FM band and going down improves the lower end. So it seems they have picked a pretty good balanced value.
Has anybody tried tweaking the ant. components on their shield?
I ask because when I look at the ANTCAP value being reported by the radio I always get a value of 1 across the FM band and usually a value of 255 on the AM band. I have seen it tune once or twice in the AM band with a value around 20-30 when it hit a strong station.
The antenna design app note states that with a proper L1 value the variactor (ANTCAP) value should stay in the middle of it’s range (1-191) thru out the tuning range. Also states that if it stays at 1 then the value of L1 needs to go down. I’ve tried going down as low as 47nH but if anything the tuning seems worse and the value is still 1.
Has anyone else done any testing along these lines?
Hi, I picked up a couple of these chips and a Shield last week. Sparkfun is local for me. I didn’t even know this until I found a link to this chip and went to order it. It’s just a pickup counter but they had a lot of stuff on display in the lobby along with a vending machine with about 2 dozen of their products in it. Very cool!
Aimee, who processed my order said they want to get these installed on college campuses and places like that. Neat idea.
Anyway, for those people looking for a Si4735 breakout, the shield may be an Arduino compatible format but that doesn’t mean you can’t use it with other MCUs and Dev boards. I bought it to proto a board I am laying out to stack on a MikroElectronika SmartGLCD240x128. This is a touch screen display with an on-board pic 18F8722. It runs at 5V but has 3.3V on board too.
Which brings us to the first problem. The Shield is 3.3V device. It does have translation(protection) for all the inputs to the Si4735. However, the SDI output from the Si4735 does not have translation. You may or may not have a problem reading this with a 5V MCU. I did have a problem. Fortunately my board has a microSD card socket that is wired thru a translator that I was able to usurp.
Because of the way the Shield is wired you have to communicate with the radio using SPI. This is really not an issue because if you look at the three com schemes you can use, SPI is the easiest.
If you are writing your own libraies and you reference the Arduino library you will see it states that you have to drive the GPIO lines after power up to select this com mode. This is NOT true. The shield has a pullup on one of the select lines and the chip as a built in for the other. This matters because one of these pins is also the SDI line. This will normally be an output to your MCU. To drive this as the library states you need to make your MCU pin an output. If your using a 5V MCU you would be putting 5V on the radios 3.3V i/o pin. And if your using translation then it would need to be bi-directional on this line. Fortunately you do not need to do this. The pullups will hold the pins in the proper state to select SPI mode. The MCU just has to wait a bit longer then if they are being driven.
Those are really the only issue you will have using the Shield with other devices. For me it’s just a stepping stone to a final board but if your looking to add a radio to a project it a great little board and the chip is just amazing!
It saves a lot on the hardware side but the firmware end can be pretty daunting to get a handle on all the features. You have about 1000 pages of data sheets and RBDS standard to wade through to find the pertinent data. But it’s pretty easy once you know how it works.
After about a week of effort I have a fully functioning radio with RDS display. Pretty cool chip and you can program some real cool features once you know how the RDS works. Like search for and preset only rock stations, or automatically tune to an alternate frequencies if the signal gets bad. Cool possibilities.
So if your looking to play with this chip, don’t let the Shield form factor deter you. And if you happen to use MikoBasic Pro I have a pretty complete library although it’s still pretty beta at this point for the higher functions.
We’ll there is supposed to be a nation wide ‘emergency broadcast’ at noon to test the homeland security system. If this thing is working right I expect the genre display to say ALERT! and the RDS to display to the emergency info. Again, cool chip and great timing on the governments part for once!
For the other hackers out there I hope it helps.
No public wish lists :(