Re: Hacking the HP45
Posted: Mon Jul 11, 2016 5:48 pm
A quick update. I have not been uploading to the forum for a while, there are several reasons.
1. Some things got in the way that kept me busy. This is something between work, a good contest on Instructables and a wedding present that is proving to be quite a handful. The project for contest on Instructables is almost done. The wedding present is coming along nicely, but requires 2 more weeks.
2. The HP45 project had a bit of a stumbling block. The issue was described in a previous post. The MIC5891 chips did a great job driving 12V, but they had 2 issues. They cannot run at 3.3V, so they would already need a level shifter for 3.3V use and they take forever to shut down if they have no load.
The later is the biggest problem. Without some pulldown resistors, the MIC5891 would simply not close in time (taking in the hundreds of microseconds). I tried to add 22 pulldowns to the board, but there simply is no space left. I would either have to widen the board again, or find something else.
The backup plan was the old plan. 3 4017 chips. They cannot run with 3.3V inputs if they run at 12V, so the above mentioned level shifters are required. This is the part that took me so long. Building a good level shifter. I settled on the N-channel mosfet way. It is bi-directional, but I only care about the fact that it works. The initial results are looking good. Floating outputs take 2 microseconds to close. This is more than acceptable.
I still need to test whether it works with the HP45 in place and whether it will work on 3.3V, but it already looks better than the MIC5891. It will take a while before I can pick this project up again, but this is the current status. Also note that I will have my holiday somewhere next month.
1. Some things got in the way that kept me busy. This is something between work, a good contest on Instructables and a wedding present that is proving to be quite a handful. The project for contest on Instructables is almost done. The wedding present is coming along nicely, but requires 2 more weeks.
2. The HP45 project had a bit of a stumbling block. The issue was described in a previous post. The MIC5891 chips did a great job driving 12V, but they had 2 issues. They cannot run at 3.3V, so they would already need a level shifter for 3.3V use and they take forever to shut down if they have no load.
The later is the biggest problem. Without some pulldown resistors, the MIC5891 would simply not close in time (taking in the hundreds of microseconds). I tried to add 22 pulldowns to the board, but there simply is no space left. I would either have to widen the board again, or find something else.
The backup plan was the old plan. 3 4017 chips. They cannot run with 3.3V inputs if they run at 12V, so the above mentioned level shifters are required. This is the part that took me so long. Building a good level shifter. I settled on the N-channel mosfet way. It is bi-directional, but I only care about the fact that it works. The initial results are looking good. Floating outputs take 2 microseconds to close. This is more than acceptable.
I still need to test whether it works with the HP45 in place and whether it will work on 3.3V, but it already looks better than the MIC5891. It will take a while before I can pick this project up again, but this is the current status. Also note that I will have my holiday somewhere next month.