Microcontroller 8051 with RF-tx and rx and encoder and decoder - Electronic Circuits Projects Diagrams Free

ashishdaga1 · 23rd May 2008, 03:23 PM

guys help me out plz.i have set up a rf tx and rx using 8051 along with ht640 encoder and ht648l decoder,TX and RX-315Mhz from vegakit.
here is my circuit diagram

the problem is when i connect the 8051 to the encoder the data send is not received at the receiver but as soon as the 8051 connections are removed the transmisison works perfectly.
thus manually the RF communication works perfectly i.e the 8 bit data which i give manually at the encoder is perfectly send and then later received at the decoder side
Is some sort of interfacing required b/w encoder-ht640 and microcontroller 8051 or at the receiver side b/w the decoder-ht648l and 8051 .help me plz its urgent

ericgibbs · 23rd May 2008, 04:34 PM

hi,
The datasheet for the ht648l decoder says its compatible with the MCU.

A common problem is, you may have set the MCU port pins as OUTPUTs within the program.?

Papabravo · 23rd May 2008, 04:58 PM

In the 8051 architecture ports 1,2, & 3 are quasi-bi-directional ports. They have weak pullups, and no data direction registers. They require no configuration and have 1's written to them at reset making them inputs or "weak" 1's They will sink a couple of milliamps, but source only several tens of microamps.

Now here is the GOTCHA. Port 0 has OPEN DRAIN outputs. There is no weak pullup inside the chip, you gotta have external pullup resistors!

ashishdaga1 · 24th May 2008, 02:38 AM

Quote:

Originally Posted by Papabravo

In the 8051 architecture ports 1,2, & 3 are quasi-bi-directional ports. They have weak pullups, and no data direction registers. They require no configuration and have 1's written to them at reset making them inputs or "weak" 1's They will sink a couple of milliamps, but source only several tens of microamps.

Now here is the GOTCHA. Port 0 has OPEN DRAIN outputs. There is no weak pullup inside the chip, you gotta have external pullup resistors!

i have connected external pull up at port0 but problem is that the interfacing the transmitted data is not been able to decode.
i checked it separately also i.e only 8051 connected to encoder and TX and only the decoder and RX at the other end but the decoder is not able to read the data send by the 8051 through the encoder.
mic->encoder->tx rx->decoder
this does not seem to work also

is some sort of interfacing required to connect 8051 to another IC?????

Papabravo · 24th May 2008, 03:07 AM

Have you looked at the RF output with an oscilliscope? Can you get your hands on a working receiver to test the transmitter? Can you get your hands on a working transmitter to test the receiver?

blueroomelectronics · 24th May 2008, 04:07 AM

Just curious, is the transistor "From Tree" supposed to short VCC to GND?

ashishdaga1 · 24th May 2008, 04:29 AM

Quote:

Originally Posted by blueroomelectronics

Just curious, is the transistor "From Tree" supposed to short VCC to GND?

no its acting as an inverter so when "from tree" is vcc P3.6 is gnd and when "from tree " becomes gnd P3.6 is vcc.this is to monitor external events and i am checking p3.6 in my 8051.as of now this is not connected in my circuit but will be added later.presently i am concerned with
mic->encoder->tx

rx->decoder

the above does not seem to work so is any sort of interfacing required b/w ports of 8051 and the encoder

blueroomelectronics · 24th May 2008, 04:57 AM

Do you have an Oscilloscope or Logic analyzer? Even a logic probe or heaven forbid an 8051 ICE? What tools do you have for testing your circuit?

Papabravo · 24th May 2008, 02:14 PM

Quote:

Originally Posted by ashishdaga1

no its acting as an inverter so when "from tree" is vcc P3.6 is gnd and when "from tree " becomes gnd P3.6 is vcc.this is to monitor external events and i am checking p3.6 in my 8051....

Then you dont want to connect the collector of the transistor to Vcc. Just connect it to P3.6. As I explained above there is an internal weak pullup that will pull P3.6 to Vcc when the transistor is off.

Papabravo · 24th May 2008, 02:27 PM

A cursory review of the HOLTEK HT640 Datasheet reveals the the TE pin on the HT640 is a CMOS input which is pulled low. This is problematic since the 8051 has outputs with a weak pullup. When the 8051 pin P3.3 is at a '1' this will form a voltage divider and the actual level on the P3.3/TE net will depend on the relative magnitude of the pullup and the pulldown. When P3.3 is low all will be fine and you should get a solid low.

I recommend that you insert a CMOS buffer between P3.3 and TE. I don't know if PORT 0 with external pullups might not have the same problem.

http://www.onsemi.com/pub_link/Colla...VHC1GT50-D.PDF

Just to be super picky, downright arrogant, and altogether disagreeable I'd like to point out that your schematic has no pin numbers on it. How on earth would you ever be able to tell if the board was wired correctly?

blueroomelectronics · 24th May 2008, 02:32 PM

Well it does have the "Prakash" seal of approval

Papabravo · 24th May 2008, 02:36 PM

Quote:

Originally Posted by blueroomelectronics

Well it does have the "Prakash" seal of approval

Are they also super picky, downright arrogant, and altogether disagreeable?

I do so love the rhyme and meter of Kipling.
Bill, you can be the crocodile while I play the bi-colored python rock snake.

It just occurred to me that the same problem may occur on P3.2/VT with respect to the receiver. Time to check the datasheet.
EDIT: Nope VT is a plain old CMOS active high output.

blueroomelectronics · 24th May 2008, 02:47 PM

Why not connect the RF units directly to the microcontroller? What's the point of the HT640 & HT648?

**Nigel Goodwin** · 24th May 2008, 02:53 PM

Quote:

Originally Posted by blueroomelectronics

Why not connect the RF units directly to the microcontroller? What's the point of the HT640 & HT648?

I thought they were for non-micro-controller applications?.

Simpler to remove them and do Manchester coding/decoding in software.

blueroomelectronics · 24th May 2008, 02:55 PM

Quote:

Originally Posted by Nigel Goodwin

I thought they were for non-micro-controller applications?.

Simpler to remove them and do Manchester coding/decoding in software.

That's what I thought, saves a bucket of I/O too.

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23rd May 2008, 03:23 PM	(permalink)
ashishdaga1	Microcontroller 8051 with RF-tx and rx and encoder and decoder guys help me out plz.i have set up a rf tx and rx using 8051 along with ht640 encoder and ht648l decoder,TX and RX-315Mhz from vegakit. here is my circuit diagram the problem is when i connect the 8051 to the encoder the data send is not received at the receiver but as soon as the 8051 connections are removed the transmisison works perfectly. thus manually the RF communication works perfectly i.e the 8 bit data which i give manually at the encoder is perfectly send and then later received at the decoder side Is some sort of interfacing required b/w encoder-ht640 and microcontroller 8051 or at the receiver side b/w the decoder-ht648l and 8051 .help me plz its urgent

23rd May 2008, 04:34 PM	(permalink)
ericgibbs	hi, The datasheet for the ht648l decoder says its compatible with the MCU. A common problem is, you may have set the MCU port pins as OUTPUTs within the program.? __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

23rd May 2008, 04:58 PM	(permalink)
Papabravo	In the 8051 architecture ports 1,2, & 3 are quasi-bi-directional ports. They have weak pullups, and no data direction registers. They require no configuration and have 1's written to them at reset making them inputs or "weak" 1's They will sink a couple of milliamps, but source only several tens of microamps. Now here is the GOTCHA. Port 0 has OPEN DRAIN outputs. There is no weak pullup inside the chip, you gotta have external pullup resistors! __________________ We never have time to do it right; but we always have time to do it over.

24th May 2008, 03:07 AM	(permalink)
Papabravo	Have you looked at the RF output with an oscilliscope? Can you get your hands on a working receiver to test the transmitter? Can you get your hands on a working transmitter to test the receiver? __________________ We never have time to do it right; but we always have time to do it over.

24th May 2008, 04:07 AM	(permalink)
blueroomelectronics	Just curious, is the transistor "From Tree" supposed to short VCC to GND? __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

24th May 2008, 04:57 AM	(permalink)
blueroomelectronics	Do you have an Oscilloscope or Logic analyzer? Even a logic probe or heaven forbid an 8051 ICE? What tools do you have for testing your circuit? __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

24th May 2008, 02:27 PM	(permalink)
Papabravo	A cursory review of the HOLTEK HT640 Datasheet reveals the the TE pin on the HT640 is a CMOS input which is pulled low. This is problematic since the 8051 has outputs with a weak pullup. When the 8051 pin P3.3 is at a '1' this will form a voltage divider and the actual level on the P3.3/TE net will depend on the relative magnitude of the pullup and the pulldown. When P3.3 is low all will be fine and you should get a solid low. I recommend that you insert a CMOS buffer between P3.3 and TE. I don't know if PORT 0 with external pullups might not have the same problem. http://www.onsemi.com/pub_link/Colla...VHC1GT50-D.PDF Just to be super picky, downright arrogant, and altogether disagreeable I'd like to point out that your schematic has no pin numbers on it. How on earth would you ever be able to tell if the board was wired correctly? __________________ We never have time to do it right; but we always have time to do it over. Last edited by Papabravo; 24th May 2008 at 02:31 PM.

24th May 2008, 02:32 PM	(permalink)
blueroomelectronics	Well it does have the "Prakash" seal of approval __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

24th May 2008, 02:47 PM	(permalink)
blueroomelectronics	Why not connect the RF units directly to the microcontroller? What's the point of the HT640 & HT648? __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com Last edited by blueroomelectronics; 24th May 2008 at 02:48 PM.