Hi,

As a project with my ASURO I am replacing the processor and need a 5volt supply.
I plan to do this by using a 9v battery and 7805 regulator. (This will be a permanent modification)

I have studied the H-Bridge that powers the motors and it seems like I could power the motors directly off the 9v battery since I read the specs of Igarashi 2025-02 is 9-12v and 3-12v on another webpage.

What do you recommend, should I cut some tracks and run the motors directly off the battery or just power everything off the 5volt rail?

Thanks

Answering my own question, 5 Volts works fine. Thanks anyway.

The motors might accept up to 12v . But the H-bridge circuit does not support those voltages. The PNP transistors (T1,T3,T5,T7) used in the upper part of the bridges are switched directly by the Atmega8 chip. So, as maximum the base of these transistors is on 5.5v. (maximum safe rating of the chip). In your case this would be only 5v due to the 7805 regulator. To make the PNP transistors fully shut-off (no collector current) the collector needs to be at a voltage less than a diode voltage drop above it. If the H-bridge would be sourced by a secondary battery voltage higher than lets say 6.1 volt (or 5.6 with your 7805 regulator) then the bridge wouldn't be able to close correctly and burn through when the lower transistors are passing current too. Basically you've got a real HOT-ROD then!

If you wanted to supply the motors with higher voltages then I suggest you replace the H-bridge circuit completely.

If you can read the German language then you might find some usefull information on this forum:

http://www.roboternetz.de/community/thr ... ght=racing

There are several threads about attempts to improve Asuro's running speed. You might want to do a search.

P.S. Don't be fooled by the 9v means more power idea. Those small 9 volt block batteries have alot less capacity than those AA or AAA battery packs. So, Asuro would run a lot shorter in time. A six-pack of AAA rechargeable (to supply a 7805 with barely enough 7.2 volt ) would get you further. And aside from that, all a 7805 regulator does is burn off the excess 4 volts into heat. Not very efficient.

Thanks, it is a shame my processor (Teensy) is reported to be damaged by over 6volts or I would just run it from the 4xAAA pack. Sometimes brand new batteries have a charge is over 1.5 volts so I didn't want to risk it.

Plus I am powering the processor board direct from the computer via the USB cable while I am developing and that has a 5volt supply too. I have not even connected the 9volt battery yet.

I know the 7805 is inefficient which is why I considered powering the H bridge directly from 9 volts. (thanks for the warning)

Cheers

p.s. I have started getting into the German section with Google translate and have found some useful info. Never used Google translate before.

If you have Asuro powered by the USB port then I suggest you don't use the motors, or other addons that draw much current. USB specifications are that devices should not draw more than 100ma current by default, or max 500 ma when specifically requested via it's device descriptor code. (I measured my Asuro drawing about 35 ma with FirstTry program.) Whether the Teensy does or can request more power is something you need to find out yourself. If the device on the USB port draws more current then allowed then the host (pc) may shut it down.

That is why the Asuro has the jumper to short diode D9. If the jumper is not applied, then the diode burns off about 0.6 volt across it. 4 Alkaline batteries would be too much for the Atmega8 chip (5.5v max ). Shorting the diode with the jumper allows rechargable batteries to be used since the diode is now bypassed. 4 AAA batteries are normally 4.8 volt, and around 5.5v just after charging full.

So you might use a similar circuit as Asuro to reduce the voltage. 1 diode would suffice until the battery voltage has dropped off sufficiently. But the internal resistance of the battery would reduce the voltage by itself anyway if enough current flows. So it may not even be necessary to use a diode for those few tenths of a volt remaining.

Hi Valen,

Sorry I did not think of the 0.6 diode voltage drop, I thought the diode was for people using battery chargers or to protect against reverse voltage.

Yes the Teensy works ok on the USB so far. Though can you look at this modification that I have done to let me know what you think? I have not connected the battery yet, and I do plan on disconnecting USB cable before connecting battery.

Will I damage anything if I connect the board to USB power and my regulated 5volt supply at the same time?

Thanks.

The battery powered 7805 on the Asuro PCB should not feed current back up to the USB host. Which is possible if the 7805 output has a slightly higher voltage. (nominal 5 volt is never exactly 5 volt, the same goes for USB 5 volt) Whether or not this is going to damage something, I don't know. But since this is your pc I would be very reluctant to risk this.

I am a bit confused how on how the Teensy board and the Asuro PCB with 7805 will be connected together. Your images do not really explain that. Where would the 5v (USB Vbus) of Teensy connect to? Bat+ or for example OUT+. The diode would be better suited to protect the USB Vbus 5v, but that would drop it to 4.4v nominaly.

If you are using a 7805 (or similar linear regulators) then you should also have a surge-capacitor on the input side. You should read the datasheet of the 7805 to see which sort of capacitors and how much capacitance it needs. Or else it might not be able to hold a steady 5v level.

Since the above needs to be addressed first I think, I am not going to respond on your pcb modification images yet. I find it difficult to recognise the traces on it anyway.


This might be usefull info regarding USB standard: http://www.beyondlogic.org/usbnutshell/usb1.shtml

Hi Valen,

Thanks for your time,

I updated the attached images with an amended 5V mod.

I checked the datasheet for the 7805 and it says,
"1. Input cap is required if the regulator is located far from the power supply filter.
2. No output capacitor is needed for stability but it does help transient response. (If needed, use 0.1 μF, ceramic disc)."

I took that as meaning the 7805 does not need caps because I am using a battery on the input and have capacitance already on the output.
Anyway I moved C1 to the input of the regulator and C4 and C5 remain covering the the output. See updated images.

I checked and the Teensy requests 100ma from USB host and works under full load, worst can happen I presume is PC will shutdown USB power if 100ma is exceeded.

I read a bit of the USB standard, hurt my head.

Then I found this http://www.pjrc.com/teensy/external_power.html which answers the question and describes how to separate USB power from battery power. Not sure how the diode option would go since both voltages would be near 5v. I will just MAKE sure I switch off the ASURO before connecting USB to test and reprogram the robot.

So in conclusion I should have left the cct as it was, running from 6volt battery pack (dropped to 5.4v via the diode) and turn off the battery before connecting to USB.