campbell
Newbie level 2
Hello,
I am working on a tracking system for an amateur high altitude balloon. Basically I am taking NEMA sentences from a GPS reciever and using a microcontroller to create an APRS packet and encoding it into AX.25 (BELL202) audio frequency keying tones. Everything works great up to there. I can connect my output into my computer's sound card and the packets are received perfectly.
However, when I connect the audio output into the mic jack of a PX-777 radio (ground on sleeve, signal on ring) as soon as the radio is triggered the voltage across my power supply drops and the microcontroller resets continually, the only signal that is transmitted is a high pitched whine. I cannot figure out what is going wrong, I have tried adding series resistance to the audio output, using a low pass filter, and even buffering the output with an OPAMP. But every time the radio is triggered the whole system goes haywire.
Any general advice on connecting audio circuits to handheld radios may be of use.
Added after 1 hours 34 minutes:
Ok... as per usual after trying all kinds of fixes and doing hours of trouble shooting the system sprang to life twenty seconds after posting my first message. I think I have found the problem... please let me know if this makes sense. When I run the radio off its battery the voltage goes crazy and it fails... when I run it on dc power (or the battery for the first minute or so after it is fully charged) it works. My hypothesis is that the charge difference between the radio's ground and the system's ground is so great that when they are connected instead of equalizing they cause a disruptive current to flow. When both systems are running off of dc wall warts the ground is the same and no problems arise. If this is the case I am in the clear because in the final design all the onboard electronics will run off one bank of batteries so the ground will be shared.
I am not sure if this makes any sense, I have never encountered a problem like this before when interfaceing.
I am working on a tracking system for an amateur high altitude balloon. Basically I am taking NEMA sentences from a GPS reciever and using a microcontroller to create an APRS packet and encoding it into AX.25 (BELL202) audio frequency keying tones. Everything works great up to there. I can connect my output into my computer's sound card and the packets are received perfectly.
However, when I connect the audio output into the mic jack of a PX-777 radio (ground on sleeve, signal on ring) as soon as the radio is triggered the voltage across my power supply drops and the microcontroller resets continually, the only signal that is transmitted is a high pitched whine. I cannot figure out what is going wrong, I have tried adding series resistance to the audio output, using a low pass filter, and even buffering the output with an OPAMP. But every time the radio is triggered the whole system goes haywire.
Any general advice on connecting audio circuits to handheld radios may be of use.
Added after 1 hours 34 minutes:
Ok... as per usual after trying all kinds of fixes and doing hours of trouble shooting the system sprang to life twenty seconds after posting my first message. I think I have found the problem... please let me know if this makes sense. When I run the radio off its battery the voltage goes crazy and it fails... when I run it on dc power (or the battery for the first minute or so after it is fully charged) it works. My hypothesis is that the charge difference between the radio's ground and the system's ground is so great that when they are connected instead of equalizing they cause a disruptive current to flow. When both systems are running off of dc wall warts the ground is the same and no problems arise. If this is the case I am in the clear because in the final design all the onboard electronics will run off one bank of batteries so the ground will be shared.
I am not sure if this makes any sense, I have never encountered a problem like this before when interfaceing.
