Do you have a question on Embedded electronics and controls? Ask our Expert, Paul Clarke

Hi,

I have a project on car remote controls, are you able to point me to some articles? especially regarding the production..

Are you asking about the key fob you use to unlock the doors or remote control cars (1/8th scale) or Car remote controls in the literal sense of a car made to work by remote control, like the mythbusters like to do.  Since your asking about production , I suspect it is the keyfob your asking about.

hello sir ,
i am designing a home automation system .
the system will be simple . it will just use a remote control to switch on and swich off  devices(maximum of 64) of a house.
it is first project of my life .
please guide me .
thanks i advance.

Hello Sir Paul,

I am looking for a nice project for computer interfacing using Visual Basic, can you please help me by suggesting ideas.

Thank you!

Hi Paul,

I am designing a Duplex CAN bus architecture to be transmitted over a long cable (maximum 25 km.) with 1 conductor plus return path, which will also carry a DC voltage. What would be the best method for coupling and decoupling the data stream from the DC offset to minimise losses and maximise SNR?

Hello Raymond,

You don't quote the bit rate you need to support but I think you will have some problems:

CAN won't do 25km (at sensible bit rates) or mix with DC power using any standard physical layer.

You need a CAN modem at each end which will relay CAN traffic through the cable.

Without knowing a good bit more about the cable and bit/data rates you want to support it isn't possible to make rational suggestions about the design of the modems.

(It isn't just the CAN bit rate that matters but the actual amount of data to be transferred and acceptable latency or delay.)

(If you have deep(ish) pockets I can design this for you - it sounds quite fun ;-)

Thanks for the reply Michael. Alas, in these times of economic adversity, the "deep pocket" option isn't an option so I shall have to muddle along trawling forums and struggling through text books.

I haven't got any data on the reactance of the cable, but it has a characteristic capacitance of 0.6uF for 10000 ft. (I apologise I;m too lazy to figure that out in metric) with 100 ohms resistance (for 10000 ft.) on the forward path and 68 ohms (per 10000 ft.) on the return path.

I made an error in my original post, I meant 25000 ft. , not 25 km. Bit rate isn't enormously important, I need to multiplex 2 analog signals on one side and send a trigger from the other side. Delay could be an issue if it was significant. sub-millisecond resolution on the signals would be nice but whatever really, it's negotiable.

I suggested CAN bus as I know that this can be done, but OFDM or some other encoding would also work, it doesn't matter.

cheers.

Hello;  Kindly I have Schematic cct. for an pulser transmitter and I'd like to find person can completely build it , So how you can help or advice, I'm ready to pay the cost. thank you for help

Hello Raymond,

Is this co-ax cable - if so then what matters is the characteristic impedance and the insertion loss at the frequency you operate at. To drive this length of cable you will need to properly impedance match the transmitter and receiver. You have the added complication of the DC bias. Don't forget that 25000 ft of your cable puts (168 * 2.5 = 420) ohms in series with your power supply which may limit how much power your remote end can use.

I wouldn't use CAN for this - you have a simple master and slave topology so CAN's networking virutes are wasted and its poor use of physical bandwidth will be a problem.

When you say you want to "multiplex 2 analog signals" do you literally mean couple one and then the other to the cable or do you plan to digitsie them and transmit data back. If so then what is the analogue bandwidth and signal/noise ratio you need.

Mr. Clarke,

I have a relay and A/D board controlling my HVAC system at my house.  I have the software up an running, and it works fairly well, but I am having some trouble when the system needs to switch from heating to cooling or back.  There is a sensor in each one of 8 rooms, and if the temperature in any room is out of bounds, the system turns on the air handlers.  I have a database which sets the parameters for each room.  In addition to the sensor ID and a pair of time control parameters, there are four numbers associated with each sensor.  The first is a Boolean which determines whether the room is occupied or unoccupied.  The other three are temperature limits.  The first is the target temperature for the room when occupied.  When in heating mode, if the temperature in the room is lower than this, and the room is occupied, the room makes a call to the air handler.  In cooling mode the call is made if the temperature is higher than the target value.  The second number is the unoccupied minimum.  If the room is unoccupied, the system is in heating mode, and the temperature in the room is below this limit, the room makes a call.  The last number is the unoccupied maximum.  If the system is in cooling mode, the room is unoccupied, and the room temp is above the maximum, the call is made.  The problem manifests when the system has to decide to change from cooling mode to heating mode, or vice versa.  I've tried several approaches, and the best one so far is this:  There is a daytime and a night-time outside temperature target.  The daytime target is lower than the night target by three degrees, because the sun tends to heat the house, making it several more degrees warmer than ambient during the day.  Currently I have these set for 62F and 65F.  I then measure and record the outside temperature over the last 90 minutes.  I take the 15 minute average of temperatures 90 minutes ago, add the average tempertaure over the entire 90 minutes, and divide by two, allowing for a rapidly dropping temperature to have more weight than a slowly dropping one while still acounting for the fact there is a time lag in inside temperature trends due to the thermal mass of the interior of the house.  I then subtract the target temperature from the actual temprature in every occupied room and take the average, igoring any unoccupied rooms.  I take this number - which of course may be positive or negative, and add it to the weighted outside average.  If the resultant number is lower than the outside temperature target, then the system is switched to heating mode.

Do you have a suggestion for a better way to switch the system from heating to cooling or vice-versa?