Hey All,
For those of you with Hum / Noise issues (well everyone else actually also):
You should NOT be connecting the Audio Ground (i.e. the bare copper shield from the audio cable) to Pin number 7. This is a Signal Ground (i.e. for communications, not audio). The proper Ground for the Audio would be Pins 4 and 6 (Labelled RH- and LH- in various pictures in this thread).
So, the RH+ (Pin 3) and RH- (Pin 4) are the RIGHT AUDIO signal (+) and AUDIO ground (-)
and the LH+ (Pin 5) and LH- (Pin 6) are the LEFT AUDIO signal (+) and AUDIO ground (-)
Do not confuse the '-' or AUDIO Grounds with the chassis or power (12Volt) ground or the Signal ground - this is what is causing any humm.
Best way would be to tie the two AUDIO grounds together and to the SHIELD of your Audio cable.
As for those of you blowing up your units when trying to short Pin 13 / Pin 15 to Pin 1:
If you do not know for sure, for your particular model, that the pin (13 or 15) is the ACC (Accessory Power out) or the RES/AUX the DO NOT just connect a wire to GROUND because if the Pin you are tying to ground ends up being the ACC pin then you WILL fry your unit! (You are tying a POWER OUTPUT pin DIRECTLY to Ground - this is not a good thing to do...)
The better way to 'experiment', if you must, would be to go to Radio Shack (or other parts store) and get a in-line fuse holder and put in a small current (Amperage) value Fuse (like 0.25A, i.e. a quarter of an Amp or 250 milliamp). Now use the two wires one either side of this pig-tail fuse to tie the Pin 13 or 15 (on one side) to Pin 1 (on the other side). Now, if this ends up (after powering radio on and trying to select AUX or CD, etc.) BLOWING this 0.25 A fuse the you know that this is
NOT the pin you want to tie to Ground.
Another Idea (I haven't tried this myself yet):
In regards to the pin that IS the ACC (Accessory Power Out) - This is probably not really a Pin meant to POWER an external Accessory but more likely to 'tell' that Accessory Unit the the Radio is ON (and then the Accessory can turn itself on, but getting it's own power from it's own Power pin that is connected through a Fuse to the Vehicle +12V). Does anyone know if this Pin (ACC) goes Hi/Lo (i.e. +12V / 0V) when the radio is powered on off? Or maybe it only goes Hi (+12V) when you press an AUX or other button on the Radio face?
If this is the case then I could come up with a simple circuit that when you press the AUX button on the Radio (and ACC goes Hi) then the 'grounding' of the RES/AUX pin would occur (via a relay or transistor) - this would make it so that you could switch your AUX input On/Off via the Radio control.
Also, for those wanting to power a USB receptacle from your vehicle you could use an LM7805, which is a DC to DC converter (5V regulator), to convert the battery voltage (12V, actually nominally about 13.5V) down to 5V (which is what USB power is).
Here is the Radio Shack info:
+5V Fixed-Voltage Regulator 7805
Model: 7805 | Catalog #: 276-1770
$1.99
Here is an LM7805 circuit:
And the LM7805 device image:
You would probably want to put a pigtail fuse between the +12V and the INPUT pin of the LM7805 as well as another between the OUTPUT pin of the LM7805 and the USB port. The above LM7805 from the Shack is capable of 1.0A so you would probable want a 2A Fuse between +12 and LM7805 INPUT and a 0.5A or .75A Fuse between the LM7805 OUPUT and your USB Connector.
Here is an image of the USB connector pinout:
You would connect the LM7805 OUTPUT (through 0.75A fuse) to Pin 1 of the USB and connect Pin 4 of the USB to Vehicle Ground (also connect the GND pin of the LM7805 to Vehicle Ground).
I'll post again if I get a chance to look at this and try it over the holidays...
-Waltf (Electrical Engineer)