Additional basic stamp servo power supply

[John Gutmann]

I have a Basic Stamp and 2 servos i want to run from it, but from a different power supply. I have a 7805 to make a 9 volt battery supply 5 volts, but I cant figure out how to get power to the servos from it, I hooked it up all the right way, but it just doesn't work

I need, power coming from a diff source then the Stamp, but the signal to come from the Stamp

[sciguy125]

I was drawing some schematics for my lab report, so I made one for you too. How do you like my 1337 p41n7 skillz?

You can use the output from the 7805 to power both the servos and the Stamp. If connect power only to Vdd, you can bypass the onboard regulator. Just make sure you use 5V lest you fry your Stamp. You can connect your i/o pin directly to the servo signal pin because it doesn't use much current. However, you mentioned to me a few days ago that you had some current issues with LEDs, so I put a 74245 in line with it in my schematic to show you how to use it. The 245 is an octal non-inverting buffer. I'm not sure about others, but the 74AC245 can handle 70mA on each output. You could also use a transistor to drive your LEDs (or whatever else), but I like to use ICs whenever I can because they're in a neat little package. They're nice if you don't need big currents.

[John Gutmann]

oops! can a modmove this some where in technical discussion? I thought i was in the right forum

[John Gutmann]

Also I figured it out, the guy on tech support told me to connect the regulator to the common groung but then i disconnect the ground from the servo when I did that( I dont know why ) but i have it connected to the servo and the regulator, nothing with vdd has changed, incase anyone elese wants to know

[Al Skierkiewicz]

Originally Posted by sparksandtabs

I have a Basic Stamp and 2 servos i want to run from it, but from a different power supply. I have a 7805 to make a 9 volt battery supply 5 volts, but I cant figure out how to get power to the servos from it, I hooked it up all the right way, but it just doesn't work

I need, power coming from a diff source then the Stamp, but the signal to come from the Stamp

There should be no reason this doesn't work as long as the negative from both power supplies and the basic stamp ground are tied together. (Including the common lead of the 7805, and the common leads of the servoes.) However, as much power as a 9 volt battery has, it is limited. You might want to get a battery holder from Radio Shack that allows you to use either AA or C cells in a 9 volt configuration.

[John Gutmann]

Originally Posted by Al Skierkiewicz

There should be no reason this doesn't work as long as the negative from both power supplies and the basic stamp ground are tied together. (Including the common lead of the 7805, and the common leads of the servoes.) However, as much power as a 9 volt battery has, it is limited. You might want to get a battery holder from Radio Shack that allows you to use either AA or C cells in a 9 volt configuration.

well I dont need 9 volts, I need 5 volts(hence the 7805) so i just need like C or D cell holders that hold 4, so i can have a long run time. i have a holder for AA's but I dont know the rating on them, if anyone one might know they are Rayovac Alkalines(I got the cheapsest ones when they were on sale)

[sanddrag]

AA, C, and D batteries all are 1.5V nominal. I'm not sure on the capacities, but obviosuly larger ones are more and they will last longer for a given draw.

I think you should put the 4 AAs in series for 6v nominal.

[John Gutmann]

yes that is the size of the holder I have, I was planning on doign that anyways, I knew the voltage but I was asking bout the AHr rating because of the chemical and brand.

[Alan Anderson]

Originally Posted by sanddrag

I think you should put the 4 AAs in series for 6v nominal.

A 7805 regulator isn't going to work very well with only 6 volts of input, and even with a "low dropout" regulator instead, the input voltage will eventually drop below 5 volts as the cells are used. To get a steady 5v supply, the suggestion to use six of them in a 9 volt configuration is more appropriate.

sparksandtabs might be able to get away without a regulator, though. The HITEC servos we use are very happy running off the unregulated 7.2v backup battery.

[John Gutmann]

well ofcourse, any battery you use will drop below 5 volts eventually, so I would have to deal with that problem no matter what

it is just the length of ime it will take, also 6 of one kind aof battery will be heavy for these servos, 2 of them just barely make it over the metal thing between bare floors and a rug(i forgot wut it is) it also kinda steers it so i know the swivel is tight


or the rug problem may be due top the crappy 1 inch caster i have on the back, it isn't a ball caster, because I know someone WILL ask

[foobert]

but the 7805 needs 7 volts in to provide 5 volts regulated.

4 cells will not do it.

[John Gutmann]

then I will use 5 cells