I have built a servo controller around a PIC Microcontroller. The servos are pwered by a 6V NiCad battery pack that also powers the PIC through an LM1117 (neither 5V nor 3.3V work reliably).
Unfortunatly, as soon as I get some load on the servos, the PIC resets due to the poer drop.
How can I make sure that the PIC will always get sufficient DC, so it won't reset?
Adding a separate battery for the PIC is not an option (space constraints).
Any help is greatly appreciated.
Matt
This sould not normally happen. Try filtering the power to the PIC and running it at 4Mhz. This should allow the PIC to keep running down to 2 volts.
If the voltage falls below 2 volts when the servos run, your battery is defective.
-- Luhan Monat (luhanis \'at\' yahoo \'dot\' com) "The future is not what it used to be..." http://members.cox.net/berniekm
Either Your wiring is wrong or your Servos are noisy, assuming that the battery is actually capable of delivering the current!
1) The wiring must be separated into a Power and a Control network, the power and return nets, for the micro and the servos meeting only at the battery. 2) You may want to filter the servos with an RC network across the terminals on each. 3) You may want to isolate the micro from the servos using relays/optocouplers. 3) is if 1 & 2 does not work.On Wed, 4 May 2005 04:39:26 +0200, "Matthias Melcher" wroth:
Add a switching DC-DC converter between the battery and the regulator to raise the battery voltage so that the input to your LM1117 doesn't drop below a value that it can regulate well at. The PIC doesn't require much current so a switched capacitor voltage doubler like the ones from Maxim should do the job.
Jim
You need to isolate the pic's power from the servo power. The servo motor is a short when it is stationary and so it kills the power supply long enough to reset the pic.Put a diode in series with the supply to the regulator and a small cap (try 10uf) from the diode cathode to 0v.
Thanks for all the help from the NG. So putting it all together, I got it checked in the skope and working! Yeah!
So here's a summay:
Problems:
- regulating 6V down to 5V is a bad idea, because of voltage drop.
- running up to 24 servos simultanously on a walker robot puts huge strain on the battery, each servo sucking up to 1Amp!
- noise!
Limitations:
- due to space and simplicity in the charging unit, it is not possible to have a second battery
Solutions:
- the voltage regulator runs through a filter, then a low drop diaode, then a cap, then the regulator, then two more caps
- Connect the regulator as close to the battery as possible, don't run the lines by a few motors first (stop thinking digital! Wire is always a resistor and a cpacitor!). Clean up the layout!
- Worst case, use a switching regulator that even pumps 3V up to 5V if need.
- a 300Ohm resistor on every servo data line in series keeps the noise from the servos to the PIC low (not neede for digital servos)
- 3k pullup on the servo data line keeps the servos from jerking all at onece when power is switched on
- I change the software to send pulses to the servos in groups of 4 with 2ms delay from group to group, so that there is only on high load (leg) servo per group. This spreads battery load over the 20ms cycle.
- with digital servos, the load on the battery is even greater. On the other hand, they are happy with 3.2V pulses. So in that case, I use a 3.2V regulator which runs more stable on 6V battery anyways.
Problem solved! Thanks for all the help!!
20uH +---+ Bat ---UUUU---|>|--o--|reg|--o---o--> pic | +---+ | | === | === === 470uF| | 10u| |.1uF GND ---------------o----o----o---o--> GNDElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.