Simple circuit

[RMParkhouse]

Iv wired up a simple circuit to test my new 18x chip, the chip is programmed to turn output 7 on when input 6 is on, output 7 is connected to an LED with a 220R resistor, the circuit is wired correctly becasue i used the same one for a 18A chip and it worked but when i turn it on the LED comes on even when the switch hasnt been pressed, and this is the weird thing, i checked the voltage and when the switch isnt pressed 2.2v is going through the output pin and when i press the switch that goes up to a full 5v (or close to it), does anyone know what ive done wrong, perhaps the circuit is slightly wrong? or maybe iv broken the chip or something? thanx in advance 4 ur help

 

[bgrabowski]

Do you have a pull down resistor on input 6?

 

[hippy]

2.2V, being nearly halfway between 0V and 5V is often indicative that there is a short to that line from somewhere.

If it's build on vero-board/strip-board, check for slithers of solder, wire-strands and solder bridges. Running a sturdy craft knife between all copper tracks will clear many shorts, and any 'kick' or jamming may indicate where a fault is.

If it's a breadboard circuit, check that wires haven't fallen over or are slighly pulled out and are shorting one another near their ends. Check that the wires really do go where expected.

If the 18X fails and an 18A or another 18X works now ( ignore earlier tests ), then it would probably be fair to say the chip itself was damaged, but the process of swapping chips can sometimes cause the fault to appear or go away, but <b>firstly </b> ...

Check for any shorts there may be. If the chip in place has been damaged and the fault remains, you don't want to damage more chips by plugging them in.

Unplug the 'faulty chip' and check what the voltage is at that pin on the socket; if it's around 2.2V you have a problem on the board.

With the power off, do a resistance check between the socket pin and 0V, 5V and all other points to which the track from that point connects.

You can then try with the PICAXE in the socket but having gently raised the leg horizontal with a pair of pliars so all but that leg is in the socket. Check the voltage on the leg; if it's 2.2V then it would seem that the PICAXE has been damaged. Otherwise, check the voltage changes as expected when the button is pushed

You can straighten the leg and plug the chip back in and measure the voltage on the pin. If it's not 2.2V the fault is intermittent or has cured itself.

 

[hippy]

bgrabowski : good point, which I missed. I always used a scope to do voltage measurements so any pulsing would be obvious and had already been discounted, and forgot that most people don't have those tools; including myself at the moment

Another possibility I didn't mention is that the LED/R isn't wired to 0V/5V as it should be but to something else on the circuit.

 

[RMParkhouse]

i put the 18x back into a tutorial board iv got and it works so i think it must be the board, im using breadboard to create the circuit and iv tried using various switches including just plain connecting it to 5V nd then pulling it out.

i just did a bit of fiddling around and i know its the board becasue its doing really strange things, for instance, if i apply pressure to the casing of the 220R resistor connected to the LED it operates as it should, im beginning to think it could be a broken breadboard problem because theres no way i can see why that would happen, maybe the resisitor is broken?

EDIT: just put a new pull-down resistor on the switch and it works but the voltage to the output pin is only 0.8v when on, is this to be expected? becasue the actual system works, the LED comes on and goes off when expected its just the low voltage is strange??

Edited by - RMParkhouse on 12/3/2005 10:33:09 AM

Edited by - RMParkhouse on 12/3/2005 10:34:50 AM

 

[RMParkhouse]

ok i got that one working so i went onto another program which shows the reading from an LDR onto a 7-seg, the program works and also operates on the tutorial board. on the breadboard the program operates as it should except when on there is only ~0.4v going out of each output pin and then ~0.12v when off, this voltage isnt even enough to light the LEDs on the seven segement, does anyone have anything i should check or maybe some probable reasons for this problem??

Also, there is 5v going into the chip becasue i can measure 5v p.d. over pins 5 and 14.

Oh and one more question, if i was to wire up a picaxe without the connectons to program it in the circuit then would i just connect pins 5 and 3 to 0v and then 14 to 5v for it to work??

Edited by - RMParkhouse on 12/3/2005 7:01:25 PM

 

[bgrabowski]

The serial in pin must be grounded and the reset pin must be connected to +V.

 

[RMParkhouse]

finally got it working with full voltage etc, was just a case of remaking the cicuit. but now i have a new problem, arent i just made of them lol. i have been downloading programs onto picaxes easily before but now it just says hardware not found on COM5. it is connected on com5, i checked on device manager, it is powered, check with a multimeter and it has a PICAXE-18 in it, also it is on the right setting and iv tried resetting it, iv even tried downloading on a different computer. is there anything else i should try before assuming the chip is broken?

 

[Rickharris]

If you have tried a second PC with no results then the fault having reread the above is still most likely on your board. check , check, check.

Are the download resistors correctly connected? Is there power to the Picaxe. these things are Very hard to kill.

 

[hippy]

Try a &quot;Hard Reset&quot;; hold the PICAXE in Reset until the &quot;Connecting to hardware ...&quot; is shown on the download pop-up. If that doesn't work, repeat but with power off until that appears, then turn power on.

As you had to remake the circuit, I don't think it would be too unreasonable to suggest that, as it was working, that the re-making has undone something else. If your board is still playing up, that could have adverse effects.

 

[RMParkhouse]

I have only been using the breadboard circuit for testing recently, I have been using PICAXE-18 tutorial board to download programs into the chip.

I have tried a hard reset and I have changed the power supply to a regulated 5v, I've even checked the chip is getting power when in the board using a multimeter.

The strange thing is when using an 18x chip it can find the hardware but I always get &quot;EEPROM verification error&quot; everytime. I thought maybe the bootstrap had been accidentally deleted on the normal 18 chip but it was working when i put it away and suddenly wouldnt when i tried re-programming. Anything else I should be checking, maybe re-installing the hardware or trying to download using a different board??

 

[HAZELEB]

Hi I have a 18x that works fine with 5v but I can only download a program into it if I change the voltage to 3.5v strange but true.