Hi,
I am trying to build simple , small, low cost peers which will be controlled by a master and will use telephone/electrical cables(live) as communication medium which are very noisy. They will do simple jobs like turning on a lamp, or dimming it, sending the temp etc. As the number will be high, the cost and being small is very important. So I am trying not to use ready made transiver ICs. The network protcol and other digital issues are not problem right now, since I am good at uPs I believe that I can manage them.
The main problem I am stuck with is its IF, interface part. After the coupler, there should be a filter, amplifier (with AGC?), signal conditioning unit for receiving and a tx unit for transmitting. The tx must be powerfull to send the signal long distances. I choose the 4800bps as the data speed and 95-140kHz band as the carrier frequency after reading some similar samples. I could not decide the modulation between ASK or FSK, there are + and - points. Also there is an alternative of using 2 carriers in the band which is selectable for noisy situations. As far as I can see, the gain should be ~60dB or more , and the attenuation of out of band signals must be high. If possible the output should be TTL in order to input to uP and receive the packets send.
I build a prototype with capacitor coupler, and using an inductor to isolate, after that, number of cmos NOT gates(CD4069) for filtering and amplification. I used ASK, in which the uP open/closes a pwm output at 132kHz in the modulation of a rs232 signal.(I use ready rs232 libs, but these can be changed of course) It is working around 30m but is not good for a perfect design since;
1-By the help of inductor the tx signal reaches 70v p-p (which I made by turn ratio), consumes much power and attenuates the received signal. From internet I found that 1A tx unit will produce around 7v p-p and working in km ranges which are using non-isolated(without inductor) or isolated design with a ratio of 1:1 , 1:2. My tx part actually a simple transistor feeding the the inductor.
2-Since there is no AGC, taking one of the peers, too close or too far affects communication. ( there is recomendation to use FSK which eliminates the need for AGC?)
3-If possible I do not want to use an inductor for cost and space
Any ideas or sample circuits similar to this?
I am trying to build simple , small, low cost peers which will be controlled by a master and will use telephone/electrical cables(live) as communication medium which are very noisy. They will do simple jobs like turning on a lamp, or dimming it, sending the temp etc. As the number will be high, the cost and being small is very important. So I am trying not to use ready made transiver ICs. The network protcol and other digital issues are not problem right now, since I am good at uPs I believe that I can manage them.
The main problem I am stuck with is its IF, interface part. After the coupler, there should be a filter, amplifier (with AGC?), signal conditioning unit for receiving and a tx unit for transmitting. The tx must be powerfull to send the signal long distances. I choose the 4800bps as the data speed and 95-140kHz band as the carrier frequency after reading some similar samples. I could not decide the modulation between ASK or FSK, there are + and - points. Also there is an alternative of using 2 carriers in the band which is selectable for noisy situations. As far as I can see, the gain should be ~60dB or more , and the attenuation of out of band signals must be high. If possible the output should be TTL in order to input to uP and receive the packets send.
I build a prototype with capacitor coupler, and using an inductor to isolate, after that, number of cmos NOT gates(CD4069) for filtering and amplification. I used ASK, in which the uP open/closes a pwm output at 132kHz in the modulation of a rs232 signal.(I use ready rs232 libs, but these can be changed of course) It is working around 30m but is not good for a perfect design since;
1-By the help of inductor the tx signal reaches 70v p-p (which I made by turn ratio), consumes much power and attenuates the received signal. From internet I found that 1A tx unit will produce around 7v p-p and working in km ranges which are using non-isolated(without inductor) or isolated design with a ratio of 1:1 , 1:2. My tx part actually a simple transistor feeding the the inductor.
2-Since there is no AGC, taking one of the peers, too close or too far affects communication. ( there is recomendation to use FSK which eliminates the need for AGC?)
3-If possible I do not want to use an inductor for cost and space
Any ideas or sample circuits similar to this?
