retepsnikrep
Senior Member
I've been working on a remote display option for my BMS which uses the simple 433mhz am transmitters and code described on this site. The BMS transmits serial data at 1200 baud to a remote display/alarm in the house. That part works very well 
I'm using an 08M at the rx end and this is all fine if the serial data keeps comming but if the Master stopped sending for some reason that would not trigger an alarm as the 08M serin would be stuck waiting for data
So in the Rx code fragment below I toggle an led on/off each time through a loop.
I added a few simple components as I did not want to use another 08M or 555 stype timer as a watchdog.
www.solarvan.co.uk/bms/RemoteDisplay01.jpg
If you look at the attached scematic you will see I am sinking an led into the 08M chip so it's on when the output is low. The circuit I added uses a simple RC to function as a simple timer on the gate of a mosfet. The gate capacitor can only discharge through the 08M when the LED output is low (LED ON). So if serin gets stuck with the ouput high (Led off) then the capacitor will slowly charge through the 1M resistor until it reaches the turn on voltage for the mosfet sounding the alarm. As long as the low pulses continue then the capacitor will be discharged through the 08M each time before it reaches the gate threshold. That's my theory. Any comments. I haven't looked at thevalues for R/C yet but I will need a delay of about 2-3 seconds before alarm sounds.
I'm using an 08M at the rx end and this is all fine if the serial data keeps comming but if the Master stopped sending for some reason that would not trigger an alarm as the 08M serin would be stuck waiting for data
So in the Rx code fragment below I toggle an led on/off each time through a loop.
I added a few simple components as I did not want to use another 08M or 555 stype timer as a watchdog.
www.solarvan.co.uk/bms/RemoteDisplay01.jpg
If you look at the attached scematic you will see I am sinking an led into the 08M chip so it's on when the output is low. The circuit I added uses a simple RC to function as a simple timer on the gate of a mosfet. The gate capacitor can only discharge through the 08M when the LED output is low (LED ON). So if serin gets stuck with the ouput high (Led off) then the capacitor will slowly charge through the 1M resistor until it reaches the turn on voltage for the mosfet sounding the alarm. As long as the low pulses continue then the capacitor will be discharged through the 08M each time before it reaches the gate threshold. That's my theory. Any comments. I haven't looked at thevalues for R/C yet but I will need a delay of about 2-3 seconds before alarm sounds.
Code:
Start:
high led
serin Rxd,N1200,("data"),b0
sertxd("Data ",b0)
low led
serout Lcd,N2400,(254,128,#b0)
goto Start
Last edited: