I am to build a circuit that operates off some kind of sound input into a sound activated circuit, preferably some kind of voice operated relay circuit. This relay is then to operate some kind of signal transmitter such as RF which activates a signal receiver and outputs onto a buzzer and an LED. It is to work something like a baby monitor, but in quite a simplified fashion, nothing too complex. I would be interested in circuit diagrams and related documents.
mail from CK
What is the max. distance between transmitter and receiver. Is it to monitor if the baby has woken up?
A sound activated switch and an FM transmitter joined together to make a voice activated FM transmitter. Set the level of sound that it will respond to. Two stage transmitter needs tuning to get best results. Tuning Kit and instructions enclosed. Transmits up to 1 km in the open depending on the aerial used. ZTX320 transistor specification.
The max distance between transmitter and receiver i would say would be no more than 20 meters or so. It should be designed to activate the transmitter when the vox detects noise up to 5m away, which would the trigger the remote alert device.
Look at a Solution here from TI (2014)
Baby Monitor is a capture and display system used to remotely watch infants. At the capture side, a microphone and a camera are placed near the child to transmit audio and video to the care giver. A parent talk-back audio system is also provided where baby can listen to the voice of caregiver.
A baby monitor is a video-based product used to see and hear an infant when the caregiver is physically not present near him/her.
I have already looked at a number of schematics and circuits i have found through my research on the internet and at my local library. I have already seen the circuit for the link that you provided, (Voice Activated FM Transmitter) and that would be ideal for the first part. I just need to know now what i would need for the receiver and remote alert unit: schematics, etc, and whether the receiver unit component values are dependant upon those of the transmitter. (All the receivers schematics I have found up to now are designed to receive speech and music like a radio…. I want to use the receiver to activate a buzzer and LED, as a remote alert device, I suppose this could also be used as a noise activated intruder alert system too!)
mail from CK
I am still trying to understand your requirement. 20 mts is quite small and is easy. What is the frequency range you need for min interference with your other gadgets. Also what are the parts your are looking at, do you need very low cost solution ? Is it just for your home use or is it for production ? will a toy circuit do ?
If you want a modern circuit, the best way is to use ready made modules. these may work at 30-200 Mhz range, some are AM some are FM.
The microphone goes to an amp which turns on one bit of the transmitter. The receiver decoded output can drive a buzzer, relay or LED as chosen.
20 meters is an adequate distance as generally the circuit is intended to be used around the house while the child is upstairs sleeping, so 20 meters should cover that quite well.
I have no other gadgets operating on radio frequencies within my home, so that should not really be a problem, i don’t think.
I would prefer, if possible, an economic solution to this, a really simple circuit would do fine, however I don’t want to purchase a ‘hobby’ kit to do this, I would prefer the circuit diagrams so I can see what parts for it i would need to get for myself…that is not a problem.
mail from CK
You must be able to study, build and test them and troubleshoot if required. i can just guide you to put things together, RF is delicate and difficult work. remember after all the efforts you put, it may not work, if you are not persistent.