View Full Version : rctime circuit w/1-5v input on the polldown
12-01-2006, 03:10 PM
I am using the rctime code circuit with a time value, I took the output voltage (1-5 volts) and put it in with the polldown resistor. seems like it works great. But the problem is, see the tranducer has three leads positive, neg and output i am using a different power supply 12vdc for the transducor, when i connect the neg lead to the bs2 vss port my time value goes to 0000 but when i just use the output lead it works good.· The real problem is when i connect the bs2 to my project with different components the neg lead from the transducor goes to grd. what's going on.
12-01-2006, 11:00 PM
·· What is the output voltage of the transducer?· If it is more than 5V you could easily damage the I/O pin on the BASIC Stamp.· I would recommend measuring this voltage and if necessary using a voltage divider to scale the output.
Parallax Tech Support
12-01-2006, 11:42 PM
the voltage is not more then 1-5volt output from the transducer the signal works great when i only connect the signal wire but when i connect grd the signal the bs2 reads oooo.
12-01-2006, 11:47 PM
Perhaps it is your RCTIME circuit?· Have you tried using what Tracy Allen has posted on his website?
Parallax Tech Support
12-03-2006, 04:15 AM
thats basicly the same circuitry that i have, i may have different component values but the same arrangement the circuit works good when i just connect the signal wire to the stamp but when i put the grd to vss the signal goes to oooo? help wanted
12-03-2006, 04:57 AM
I'm a little baffled by this problem.....so just to try and help.
I think you are having "isolation power supply" issues. What is important is....... what is powering what?
We need to know what kind of transducer you are working with.
A schematic would be useful as well.
We need to know what you are using for power supplies, the input source, and the output voltage.
I worked in automation for 6 years...and learned you can't always connect different power sources grounds. One DC ground may have a different potential than another(meaning one may not actually be at 0v.....it maybe at -0.023v...relative to each other.....which affects things). This also causes a problem with accurate readings from your sensor. Since the two power supplies have no commonality.....the output can not be read accurately from a chip on a different power supply.
I couldn't tell the possibility of damage to the Stamp without a schematic.
It should be noted....that the accuracy I'm speaking of may not be needed in your application.
Wow....I'm sorry for going on and on.......just trying to help find the problem,
12-03-2006, 09:34 AM
thank James L,good thought the bs2 i am powering with a 9 volt battery and i am useing a 12 volt power supply to power a 12 volt tranducer neg and pos, but when i bring the neg over to the basic stamp from the 12 volt power supply does that make it different so what should i do? power the basic stamp with the 12 volt power supply?
12-03-2006, 09:39 AM
You have to have a common negative supply as a reference for both the transducer and the Stamp. You can provide 12V power for the transducer and a separate 9V supply for the Stamp ... no problem, but the negative connections must be tied together. If that will cause the transducer output to be higher than the 5V level relative to ground, you will have to use a voltage divider to bring the output to below 5V before sensing it with the Stamp (or other 5V powered device).
12-03-2006, 09:46 AM
The circuit on my web site is meant for measuring voltages in the range of 5 to 15 volts. When you power your transducer from 12 volts without its ground being connected, the output is probably in fact in the ballpark of 12 volts. It might even work to some degree, and I see that you said that it "works great". But I suspect it might work better if the ground lead is connected to some solid reference.
When you do connect that to Vss, you see a reading of zero because the output of the transducer is near or even less than thd 1.3 volt Stamp threshold, and the RCTIME commmand times out and returns a value of zero. It is much easier to detect voltages that are some minimum value greater than 1.3.
What is the transducer? Maybe you could attach its (+) terminal to 12 volts, as you have it now, and its (-) terminal to a 5 volt Vdd. The transducer would then have 12-5=7 volts across it, and the transducer output would go from 1 to 5 volts with respect to Vdd, or 5 to 10 volts with respect to Vss. The RCTIME circuit could measure that. This is just hazarding a guess. Depends on your transducer and its supply current and the application. There is a SERIOUS RISK that the Stamp could be fried by the connection to 12 volts from the transducer if it is on the same Vdd supply. You could lift the (-) terminal of the transducer to +5 volts with its own regulator or precision zener diode.
Or, get an analog to digital converter.
12-03-2006, 10:56 AM
good thought James, I am using the 9 volt battery on the board of education and a 12 volt dc power supply for the transducer could that create the problem? can i disgard the 9 volt battery and take power from the 12 volt power supply and put it in the +12vdc in the vdd port and the -12vdc in the vss port, could the bs2 be damaged? Your input will be greatly appreciated thank you.
12-03-2006, 11:02 AM
can i use the 12volt power supply to power the stamp instead of the 9 volt battery?
12-04-2006, 05:55 AM
The Vdd line MUST be at 5 volts. 9 volt and 12 volt supplies connect to Vin, NOT Vdd. If you connect anything to the Vdd line greater than 5 volts, you WILL destroy the BS2.
And yes, you can use the 12 volt supply into Vin to power the stamp.