CJ

Reote Control Circuit Question
« on: June 17, 2019, 06:23:04 PM »
how does this van/wheelchair  lift circuit work?

think i got it traced right, red curved wire off transistor is as mystery as it shorts out cap, thanks for any help, sorry for the OT,

also can not figure out why pin 8 does not go to ground (negative supply voltage)

remote no longer made, 750 dollar system to replace,

« Last Edit: June 17, 2019, 07:31:46 PM by CJ »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html


PRR

Re: Reote Control Circuit Question
« Reply #1 on: June 17, 2019, 07:54:16 PM »
> why pin 8 does not go to ground (negative supply voltage)

It does, when you push the buttons, via D3 D1. This would seem to ensure "no battery drain" when not being pushed. (However the 0.2uA quiescent current would not be a drain on a ~~300mA/h 9V tranny-radio battery: over a million hours, except they rot first.)

https://www.nxp.com/docs/en/data-sheet/MC145026.pdf

CJ

Re: Reote Control Circuit Question
« Reply #2 on: June 17, 2019, 08:35:45 PM »
your right! when i press the buttons, a pulse comes out of pin 15, i guess the circuit trace is supposed to be the antenna,

i think that transistor is supposed to do something,

wonder if that red circle should really be a resistor that burned out,,,
« Last Edit: June 17, 2019, 08:48:46 PM by CJ »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

PRR

Re: Reote Control Circuit Question
« Reply #3 on: June 17, 2019, 08:50:02 PM »
Transistor presumably boosts the small signal from the chip to send it somewhere. No clue how.

CJ

Re: Reote Control Circuit Question
« Reply #4 on: June 17, 2019, 09:37:40 PM »
i bet that bent collector wire is supposed to be the coil of a tank circuit in parallel with C1 which measures about 500 pf out of circuit,,
clock freq is 250 K Hz,

just have to make coil that resonates at 500 pf tp 250 K,
« Last Edit: June 17, 2019, 09:44:34 PM by CJ »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Reote Control Circuit Question
« Reply #5 on: June 18, 2019, 03:49:21 PM »
this thing is running at about 777 Hz, how can you transmit with that low a freq, impossible, right?  ???
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

squarewave

Re: Reote Control Circuit Question
« Reply #6 on: June 18, 2019, 06:29:58 PM »
What exactly is wrong with it? How do you know the problem is the transmitter and not the receiver?

From looking at the datasheet, 777Hz is not impossible. According to the last figure and given the values in your schem, it sounds bout right actually.

CJ

Re: Reote Control Circuit Question
« Reply #7 on: June 18, 2019, 08:20:26 PM »
the chip is good, it is sending out chunks of digital, but nothing is happening on the receiving end, hopefully a schemo is on the way, somebody might have clipped the 'antenna" by the looks of things, this would be lo freq comm, like submarines and all that,  :-*
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

PRR

Re: Reote Control Circuit Question
« Reply #8 on: June 18, 2019, 08:44:14 PM »
Yes, the encoder probably makes an audio rate to drive a wire or transmitter.

How far does it transmit? If just a few feet, you "could" pick-up enough spike-peaks to decode it.

An antenna on the transmitter makes more sense.

CJ

Re: Reote Control Circuit Question
« Reply #9 on: August 02, 2019, 05:22:34 PM »
we got a DIY remote up and running,

bought a stomp box case off of evilbay, some obsolete chips from Jameco which turned out to be legit, and a transmitter off digikey for about 5 bucks,

this thing works from quite a distance,   got some switchcraft momentary switches in there and a stubby 433 mhz antenna, LED draws about 1/2 a mil for pwr indication and everything is wired so no power is consumed until a switch is pushed, like keying in a transmitter,

running off 4 AA's which has about 2500 ma-H compared to 9 volt which is about 550 ma-H,

this thing draws about 10 ma when transmitting, the transmitter will work from 1.5 V to 12 V so no regulator is needed. power output will depend on the voltage you run it at.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html


CJ

Re: Reote Control Circuit Question
« Reply #10 on: August 02, 2019, 05:51:22 PM »
the reason that no power is supplied to the encoder chip until a button is pressed is to save current, but also, if you look at the circuit, the 4 words get encoded by bringing pins 9 and 10 hi or lo,

sw 1    pin 9 = Vcc        pin 10 = 0 V
sw 2    pin 9 = 0.6 V    pin 10 = 0.6
sw 3    pin 9 = 0 V pin 10 = Vcc
sw 4    pin 9 =  Vcc  pin 10 =  Vcc

so if the chip has a full time ground, it will always be in sw 4 mode, and transmitting that word, which will keep whatever relay is attached to the decoder chip on all the time, every time the power sw is turned on, this is not good,

so by having the chip ground going through the switches,  the word attached to sw 4 will only be enabled when the button is pressed.

now there is another reason for keeping the transmitter off when no momentary sw is pressed,  this is a cmos encoder, it runs from 2.5 volts to about 18 volts,   even with the ground lifted, voltage is mysteriously appearing across pins 8 and 16 (pwr supply pins)  when this happens, the chip puts out some noise on the transmit pin which is triggering the decoder which turns on some of the output pins , there are some leakage currents somewhere that are creeping in to the encoder chip, have not figured out how, so if you hook the transmitter ground to the encoder ground, power is only available to the transmitter when you press a button. this keeps current draw low if the pwr sw is left on by accident (only the LED indicator is on which will last for 2500/.-5 = 5000 hours) .

here is the current path which shows that sw 4 does not reach pins 9 and 10 but only grounds the encoder pin 8 thru the diode.

« Last Edit: August 02, 2019, 06:15:03 PM by CJ »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Reote Control Circuit Question
« Reply #11 on: August 02, 2019, 05:57:58 PM »
here is the transmitter data sheet

this transmitter replaces the one transistor circuit in the original remote which we could not get to work.

hopefully Doug will not be opening up any garage doors down the street when he tries to get his van door to open,  as it seems to be powerful and the antenna probably helps also.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Reote Control Circuit Question
« Reply #12 on: August 02, 2019, 06:13:23 PM »
the person we built this for moved to Idaho, so we had not way to test the remote,

so we built a receiver/encoder circuit off the MC145026/7  data sheet, the 4 small LED's are the decoder output pins and the big LED means it received a word.

what ever word is received  by the decoder chip is stored in a latch so that the output pins remain at the levels they were triggered to until a new word is received.  this means you only have to hit the sw once to activate the decoder circuit instead of holding the sw down which saves power.

when we first turned on the remote, all 4 led's lit, which told us that we had to disable the transmitter until a momentary sw was pushed to keep the erroneous mystery data from upsetting things.

the receiver is the daughter board at the bottom. there are a bunch of surface mount parts on the other side.
« Last Edit: August 02, 2019, 06:18:12 PM by CJ »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Reote Control Circuit Question
« Reply #13 on: August 02, 2019, 06:46:26 PM »
time constants formed by the RC circuits on both the encoder and the decoder have to be aligned with each other.

you do not want the bottom of the discharge curve too close to the rising edge of the next bit, this you can check with a dual trace scope.  there are formulas for this on the chip data sheet.

unlike the transmitters this guy needs a 5 volt 78L05 reg as we fried one already by over voltage.

here is the receiver we used>



If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html


 

Related Topics

  Subject / Started by Replies Last post
3 Replies
1714 Views
Last post December 02, 2004, 09:07:47 AM
by isamee
21 Replies
9013 Views
Last post December 19, 2005, 02:59:37 AM
by bcarso
8 Replies
3791 Views
Last post May 04, 2009, 12:33:45 PM
by skal1
7 Replies
439 Views
Last post May 24, 2019, 11:22:24 PM
by tablebeast