jaydag71
New Member
hello all once again! today I am having some problems with understanding how to drive this particular h bridge design, because I don't fully understand how this H-bridge works, what its limitations are, etc.
The attached PDF is of close resemblance to my current config, sorry about the schematic being so bunched together, I drew it up quick with little regard to others ever viewing...the attached GIF is a very close variation (different poles and parts). The particular part choice used was taken from the cheapo radioshack rc truck pcb that I copied the H bridge design from originally. I have it replicated on a breadboard right now with changes made to the small signal transistor- in their place I have substituted with photocouplers (PC817) to isolate the pic16f876A (16f886 in final design due to its 4pwm's and many adc's) from the H bridge(s) [the second h is for the steering motor- its a cheapo radioshack servo delux!(dc motor, mechanical slide switch)] noisy switching, etc. So in essence the photocouplers on the 'big H' are driving the larger transistors, or as far as I interpreted it?
What confuses me with the big H, as compared with a more typical design like the second small signal transistor h bridge in the pdf, is the use of those additional transistors to apparently drive the larger pairs--in the original radioshack implementation, I do not believe that it was pwm'd signals from the controlling IC (that is just my guess, couldn't verify cause I scooped some parts from the pcb for my breadboard!) but rather used to simply switch stready high or low to change directions--no speed control from radio shack toys...SO, will this copied design present a problem if I was intending to use pwm from the PIC to control speed of the rear drive motor? OR, will it be no problem since the transistors they used are also able to switch up to certain freq- I just would need to figure out how to pwm from pic at suitable specs from the pwm modules?
Is this design able to produce both speed control and direction control using only the twp pins from the pic, or would it need to be modified (ie. pwm speed control, gpio for direction switching poles?)
Also, I wonder is it too much to ask for a simple code snippet (targetted for pic16f876 or 886 preferably but...) that would be able to drive this H config using two pic signals only if it is indeed a good design and able to be driven without additional circuits. As for the schematic, please ignore the whole feedback system, it is not in play at the moment and still in total rough anyways...
Thanks in advance for any tips, especially for some code example, I just want to make sure the bridge works to control both dir and speed before I finish the rest of the tweaks and go onto the feedback design...regards, jd
The attached PDF is of close resemblance to my current config, sorry about the schematic being so bunched together, I drew it up quick with little regard to others ever viewing...the attached GIF is a very close variation (different poles and parts). The particular part choice used was taken from the cheapo radioshack rc truck pcb that I copied the H bridge design from originally. I have it replicated on a breadboard right now with changes made to the small signal transistor- in their place I have substituted with photocouplers (PC817) to isolate the pic16f876A (16f886 in final design due to its 4pwm's and many adc's) from the H bridge(s) [the second h is for the steering motor- its a cheapo radioshack servo delux!(dc motor, mechanical slide switch)] noisy switching, etc. So in essence the photocouplers on the 'big H' are driving the larger transistors, or as far as I interpreted it?
What confuses me with the big H, as compared with a more typical design like the second small signal transistor h bridge in the pdf, is the use of those additional transistors to apparently drive the larger pairs--in the original radioshack implementation, I do not believe that it was pwm'd signals from the controlling IC (that is just my guess, couldn't verify cause I scooped some parts from the pcb for my breadboard!) but rather used to simply switch stready high or low to change directions--no speed control from radio shack toys...SO, will this copied design present a problem if I was intending to use pwm from the PIC to control speed of the rear drive motor? OR, will it be no problem since the transistors they used are also able to switch up to certain freq- I just would need to figure out how to pwm from pic at suitable specs from the pwm modules?
Is this design able to produce both speed control and direction control using only the twp pins from the pic, or would it need to be modified (ie. pwm speed control, gpio for direction switching poles?)
Also, I wonder is it too much to ask for a simple code snippet (targetted for pic16f876 or 886 preferably but...) that would be able to drive this H config using two pic signals only if it is indeed a good design and able to be driven without additional circuits. As for the schematic, please ignore the whole feedback system, it is not in play at the moment and still in total rough anyways...
Thanks in advance for any tips, especially for some code example, I just want to make sure the bridge works to control both dir and speed before I finish the rest of the tweaks and go onto the feedback design...regards, jd