Audioswitcher 645/10/2023 Next was to connect it up to my iPhone (without the 10K pull down) but it just didn’t sound right, I found that adding a 10K load resistor to ground solved the issue. The first thing to do was to test the microphone on the iPhone speakers (connected to the op-amp output before the 10uF cap) and it worked fine. I changed the 10uF capacitor to a 0.1uF to give a quicker response when powered up and reduced the boost to 26x for testing. The configuration above boosts the microphone’s output (which is AC coupled) by 100x and the 10K/10K divider on the non-inverting side keeps the opamp’s output at half of VCC so that when sounds are produced there will be an AC waveform (e.g with VCC/2 being 2.5V, we could get a waveform that goes 1.5V to 3.5V) just before the 220uF capacitor.Īfter doing a bit of researching and testing, I’m using a 1.5K resistor for the iPhone microphone which is what I’ve heard that’s what the iPhone uses to power it. I firstly tried a non-inverting opamp configuration but it didn’t turn out to be as good as the inverting one above. ![]() I found an LM358 op-amp inverting circuit which we’ll use to start off with (shown above). Now it’s back to making a boost circuit for the microphone, I looked around for a low cost op-amp and found the LMV358 which is just like the LM358 and it’s rail to rail. I had the Ti SN74LVC1G3157 SPDT switch on hand and it should do the trick, just hook up 3 of these for the mic and speakers. ![]() It turns out that the microphone was a little hard to hear so after removing the 1.5K resistor it sounded better but it wasn’t loud enough unless you place the mic close to your mouth.Īfter speaking with a colleague, the idea came about of being able to switch between an iPhone and the work desk phone easily, it shouldn’t be a problem since we can an analog switch to do this. The first step was to build a Snom 4P4C to TRRS cable, I used a 220 ohm resistor for protection to find the left/right speakers and then used a 1.5K resistor for the microphone. There are some headset/headphones options available, the Snom uses 4P4C / RJ9/RJ10 connectors but I’ve always got my iPhone headphones on, so I’d like be able to use them on the Snom phone. ![]() At work, we use Snom phones and we take quite a number of calls every day, when you use the handset and need to type it’s a bit difficult.
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